Washington (CNN) Two low-profile Texas brothers have donated $15 million to support Sen. Ted Cruz, a record-setting contribution that amounts to the largest known donation so far in the 2016 presidential campaign.

Farris and Dan Wilks, billionaires who made their fortunes in the West Texas fracking boom, have given $15 million of the $38 million that the pro-Cruz super PAC, Keep the Promise, will disclose in election filings next week, according to sources outside the super PAC with knowledge of the giving.

The siblings earned their riches with the sale of their company Frac Tech for $3.5 billion in 2011, and since then have shuffled large contributions to the leading social conservative nonprofit groups that aren't required to reveal their donors. But they will no longer be able to avoid detection after giving a historically large and early donation that now make the brothers two of America's most prominent political donors.

"Our country was founded on the idea that our rights come from the Creator, not the government. I'm afraid we're losing that," Farris Wilks , a 63-year-old pastor in the small town of Cisco, said in a statement to CNN. "Unless we elect a principled conservative leader ready to stand up for our values, we'll look back on what once was the land of opportunity and pass on a less prosperous nation to our children and grandchildren. That's why we need Ted Cruz."

Keep the Promise is technically four separate committees that give three families more control over their own super PAC. Most of the attention has focused on Robert Mercer, a New York hedge fund magnate who gave the second-most money to conservative groups in 2014 than any other Republican donor. Mercer has given $11 million of the $38 million raised , according to a leader of the super PACs. Another $10 million comes from Toby Neugebauer , a Houston investor and a personal friend of Cruz's. The involvement of the Wilks brothers was first reported by National Review

Friends and associates of the Wilks brothers say they are unaffected and unassuming, depicting them as hometown-loving Texans who morphed into billionaires over the course of a decade. Intensely private, those close to the pair say they are nervous about the spotlight that will shine on their church and their family thanks to the donations.

"If Dan and Farris walk into a room, they don't want ever to be known, to be announced. They just come in and sit in the back," said Luke Macias, a Texas political strategist who has worked with the family. "They are normal people. They dress normal. They show up normal."

Photos: Designers critique campaign logos Photos: Designers critique campaign logos Presidential logos can mean different things to different people. Sky Hartman, a brand designer who created Ron Paul's 2012 logo, and Ben Ostrower, a designer who worked on Bernie Sanders' logo, review some of the 2016 presidential logos. Hide Caption 1 of 12 Photos: Designers critique campaign logos Ricky Perry – Sky Hartman: Where do I even begin? The logo is overcrowded with elements that compete with each other. For example, the descender of the "P" has a shifted perspective where the star does not. Additionally, Perry is from Texas and the flag representing Texas has one star, where here he has three. I would have stuck with one star. Overall, I'd say this is 3/10.

Ben Ostrower: Trying to be the "P" to Obama's "O," it comes off as a muddled image without enough graphic simplicity or any clarity of concept. It's a confused baseball team logo.

Hide Caption 2 of 12 Photos: Designers critique campaign logos Bernie Sanders – Hartman: This particular logo is simple enough but lacks any real unique identity that would help it stand apart from the rest. The use of color is good, however. I'd give this 5/10.

Ostrower: Gonna abstain since it was one of our designs. But I can tell you that the intention (and it's not a secret) was to make the campaign friendly, accessible and unmistakably American. In short: the furthest thing from radical or unfamiliar. Hide Caption 3 of 12 Photos: Designers critique campaign logos Carly Fiorina – Hartman: This is nice. The use of a thinner font is what makes this logo stand apart from the others. The juxtaposition of the name with the title helps to create contrast and focus the attention on who is running. The detail on the "A" isn't exactly useful but it does help to bring color into the wordmark. I'd give this a 6/10.

Ostrower: Obviously trying to play up her tech bona fides with the clean, simple typography and futuristic, angular "A." It succeeds in its simplicity (always a good thing in branding), but fails to make a significant impact.

Hide Caption 4 of 12 Photos: Designers critique campaign logos Hillary Clinton – Hartman: This logo has been the subject of much debate since first debuting. Although I respect and admire the agency that created it, I'm not so certain this conveys the right message. The use of red as the hero color seems odd for the campaign. Another odd choice is that the arrow points right and is over top of the blue. However, what is smart is the campaign walked away from her name as the focus and moved to a symbol. The brand then becomes more versatile and easier to recognize. People will walk away and remember the "H". Whether you like it or not, it's smart. Overall I'd give this a 7/10.

Ostrower: I've loved this from the start even when everyone was making fun of it. Hillary has nearly 100% name recognition nationally, so the designers had both the luxury and the obligation to take a bold risk. The result is not only iconic but highly modular: its square orientation makes it optimal for the multitude of social media uses. My favorite use of it is as a window (transparent over an image)

Hide Caption 5 of 12 Photos: Designers critique campaign logos Lindsey Graham – Hartman: This seems fairly simple although there isn't anything special about it. The lines above the name don't seem to convey anything specific. Overall it is a bit bland. I'd give this a 4/10.

Ostrower: More befitting a Senate campaign, it lacks the dynamism to inspire on a national level. The serif font unfortunately reinforces his age, his seniority and old ideas.

Hide Caption 6 of 12 Photos: Designers critique campaign logos Rick Santorum – Hartman: One thing I've noticed is the use of Gotham-style fonts. The problem I have with this logo is the kerning. The letters are a bit too close together, which when scaled down, can be difficult to read. Although the use of an eagle representing America is a good concept, I think it could have been executed better. I'd give this a 5/10

Ostrower: This is the same logo from his 2012 campaign. The red eagle feels fascistic and, frankly, a bit too much like low-rent clip art.

Hide Caption 7 of 12 Photos: Designers critique campaign logos Mike Huckabee – Hartman: One thing that was memorable about Obama's '08 campaign logo was the sun rising behind a field. It looks like the campaign took a page out of that book -- but didn't quite deliver. Although the use of type is clean and easy to understand, there's nothing about this logo that would make me remember it in two years. Overall, a 4/10.

Ostrower: Too much going on here. Sagi Haviv from the famous branding firm Chermayeff, Geismar & Haviv (also a client of ours) said it's too much of an over-engineered play on the rolling meadows of Obama's circle logo. I happen to agree.

Hide Caption 8 of 12 Photos: Designers critique campaign logos Marco Rubio – Hartman: The type treatment is clean and easy to read; however, the illustration of America as the dot in the letter "i" is very hard to see when scaled down. Overall, this a decent logo. I'd give it a 6/10.

Ostrower: This logo has taken a lot of heat. I don't love it, but I think it succeeds well enough in its obvious goals: being youthful, new and friendly. The simple sans serif and all lower case typography helps to achieve this. The small U.S. shape (sans Alaska and Hawaii) above the "I" makes it feel a little too cutesy.

Hide Caption 9 of 12 Photos: Designers critique campaign logos Martin O'Malley – Hartman: This logo seems more suited for messaging or chat app than for a presidential candidate. The main problem with this logo is that it doesn't stand out and doesn't have anything representing America. Overall, I'd give this a 2/10.

Ostrower: I've seen people say that this looks like the logo for Martin O'Malley's MSNBC show and I have to agree. I like that they were trying something a bit different here (a speech bubble!), but the execution is a bit rough. The spacing around the typography isn't consistent and the arrow element in the bottom left is at an odd angle.

Hide Caption 10 of 12 Photos: Designers critique campaign logos Rand Paul – Hartman: This logo is using a bolder font which helps the name stand out. I do like the use of negative space to represent the base of the torch but it doesn't quite have that uniqueness that makes a presidential logo perfect. Overall, I'd give this a 7/10.

Ostrower: Graphically, this is strong. Simple lettering. The negative space between the "A" and the "N" cleverly creates the base of a torch. However, the red and black colors and heavy lettering unintentionally come off as a bit fascist.

Hide Caption 11 of 12 Photos: Designers critique campaign logos Ted Cruz – Ostrower: The first time I saw this I thought the logomark looked like a tear or a drop of oil and now I can't unsee it.

Hartman: I'm not crazy about the type or the flame. The type says old and the flame seems odd. The star, which is representative of America, under the flame almost comes across as though the campaign wants to put America out. I'm certain that's not the campaign's goal, but that's how it reads. Overall, this is my least favorite logo. I'd give this a 2/10.

Hide Caption 12 of 12

Several other Republican donors will make seven-digit contributions to super PACs, which can accept unlimited donations, that will dwarf sums recorded in 2012: Norman Braman, a Florida auto dealer, will reportedly give up to $10 million to Marco Rubio's. Several Jeb Bush supporters are expected to have given $1 million to his and to be eager to give more. But the Wilks family's $15 million donation -- split between two people -- is likely to be the largest gift to a candidate on next week's reports.

Unlike some other mega-donors with an affinity for the ideological slugfest, the brothers shun giving that is meant purely for firepower in partisan fights. They choose specific projects over broad platforms. Through their $100 million family philanthropy, The Thirteen Foundation, the brothers gave nearly $19 million as part of their tithing to religious and conservative nonprofit groups like the Family Research Council and Online for Life in 2013, according to the most recent tax filings.

Driven mostly by their opposition to abortion and their fear that their religious sect -- which interprets every word of the Bible literally -- is under attack, Dan and Farris Wilks have slowly become more accustomed to funding campaigns. As recent billionaires, however, they haven't yet risen to the profile of the other conservative siblings that have revolutionized outside spending: the Koch Brothers.

Now, though, they are prepared to step right into the middle of a potentially nasty Republican nomination fight that could cost hundreds of millions of dollars.

"We need a true leader in Washington," Farris' younger brother, Dan, 59, said in the statement. "A leader that will stand up for biblical morals. We need a leader who is proud of America, not one who apologizes for us. We need a leader who encourages hard work, not one who tells people who don't work that they should make the same living as people who do. We need a leader who will make sure America doesn't end up a socialist nation."

Born to a poor family that once lived in a former goat shed, Farris and Dan Wilks spent their careers as brick-builders with their own masonry business. In 2002, they founded Frac Tech, which became one of the best positioned companies to capitalize on the growth of fracking, a controversial practice that involves the removal of natural gas or oil from rock formations.

Slowly, they marched toward a bigger role in the fracking industry. When competing Texas frackers looked to freeze the brothers out from the companies that distribute the sand needed to drill, the siblings opened their own sand quarry to thrive. Just as the West Texas fracking business began to boom, the brothers invested in their own line of trucks and became some of the largest fracking truck-producers in the country.

In 2011, they cashed out -- and began to buy enormous amounts of land in Montana for elk hunting and fly fishing. As of last year, they owned more than 310,000 acres of land in the state, making them Montana's largest private landowners, according to The Billings Gazette.

At the heart of their life, still, is the Assembly of Yahweh , which preaches a mix of Christianity and Judaism and holds the Bible as infallible. A different Wilks family member gives a sermon many Saturdays. Last week , it was Farris' turn.

"He was a pastor before he was a billionaire and he continues to pastor after being a billionaire," said Mat Staver, a prominent conservative activist close with the family.

It is not yet clear how the brothers plan to spend their money in the Cruz super PAC, or whether any strings are attached to the $15 million contribution. But the pair are said to have a particular desire to fund breakthroughs in social media and digital organizing, eyeing long-term opportunities to mobilize Christian voters on emerging or created-from-scratch platforms online.

Much of their giving is directed by Jon Francis, a family son in-law who heads The Thirteen Foundation, but those who have pitched projects to the brothers say that their philanthropy is very much a family affair. It is not uncommon for entrepreneurs to face questions from a half-dozen Wilks family members when asking for money.

Photos: 2016 campaign merchandise Photos: 2016 campaign merchandise Rand Paul's merchandise for sale includes a "filibuster starter pack" and "Rand on a Stick." Hide Caption 1 of 4 Photos: 2016 campaign merchandise Ted Cruz's merchandise features a car bumper sticker that says "This vehicle makes right turns only." Hide Caption 2 of 4 Photos: 2016 campaign merchandise Hillary Clinton's often known for her colorful pantsuits, making the "Everyday Pantsuit" T-shirt an original add to her merchandise for sale. Hide Caption 3 of 4 Photos: 2016 campaign merchandise Bernie Sanders' merchandise store features a bumper sticker saying, "You know you wanna" vote for Bernie. Hide Caption 4 of 4

That includes Republican presidential candidates. The brothers have been familiar with Cruz since he used the office of Texas solicitor general to launch several high-profile legal fights to defend Christian causes. But other Republican presidential candidates, aware of the Wilkses' net worth, have nevertheless courted their checkbook. The candidates most aggressively pining for their support, according to multiple people familiar with the outreach, were Wisconsin governor Scott Walker and former Arkansas governor Mike Huckabee.

The Wilks family's eventual pledge to Cruz was driven by his emphasis on preserving Christian organizations' ability to operate amid cultural victories for the left. But it was also motivated by the Texas senator's ability to speak about policy in the entrepreneurial terms that the brothers use when evaluating projects.

"One of the pleasures of doing business with them is they kind of treat like you like you might be the next Wilks," said Jeremy Boering, a California filmmaker who has successfully won grants from them.

Boering said that's the philosophy that Cruz pitched to Farris Wilks -- and why he's funding him.

"He thinks he's one of the only guys in the movement that seems to authentically wants to preserve the market, authentically preserve the way of life that allows people to move from bricking walls to being a billionaire," Boering said.