Some of the nation's wealthiest donors are writing multimillion-dollar checks to support candidates during this midterm season in high stakes contests across the country.

While it's not unusual for uber-wealthy donors to gild the coffers of preferred candidates, the roster of rich donors often offers a glimpse of who is playing the role of kingmaker in elections and, sometimes, who might be interested in ensuring that their political interests are heard. By the end of 2014, just five donors poured nearly $135 million into federal elections, according to an analysis of Federal Election Commission data by the Center for Responsive Politics.

So far this election cycle, 17 megadonors have given more than $100 million to candidates, party committees, super PACs, and outside groups. And six people have spent nearly more than $67 million so far this cycle in the battle to control Congress.

Here are the top six contributors thus far.

1. Richard Uihlein: $25.3 million

The single biggest donor this election cycle, Richard “Dick” Uihlein, has quickly become a GOP power player in the past couple of years.

He and his wife Liz Uihlein, co-founders of Wisconsin-based shipping company Uline, together donated more than $25 million already so far this election cycle.

Uihlein’s biggest focus so far this cycle has been on supporting Republican Kevin Nicholson's bid to unseat Democratic incumbent Sen. Tammy Baldwin in the Wisconsin Senate race. He is involved in almost every single one of the top spending super PACs supporting Nicholson.

Pretty early on in the election cycle, Uihlein dropped seven-figure checks totaling $3.5 million to a single-candidate super PAC operating exclusively in support of Nicholson called Solutions for Wisconsin. Two of the biggest spenders in the race, Americas PAC and Restoration PAC, are also almost exclusively funded by Uihlein.

Outside groups funded by Uihlein together have spent more than $6.1 million in the Wisconsin Senate race so far this year and pro-Baldwin groups have ramped up their spending to try and compete.

The face-off has resulted in a pricey contest that has attracted the largest amount of spending from outside groups. The Wisconsin race has already seen nearly $10 million in outside money.

2. Tom Steyer: $16 million

California billionaire Tom Steyer, who topped individual contributions two consecutive election cycles in a row, is leading the charge from the Democratic side again.

So far this election cycle, Tom Steyer and his wife Kathryn Steyer together have donated nearly $16 million, and the number is expected to only go up. A leading voice in the “impeach Trump now” movement, Tom Steyer has pledged to pour an additional $30 million to flipping the lower chamber to a Democratic majority.

Steyer has been active in donating money directly to campaigns, but the vast majority of his big checks have gone to NextGen Climate Action, a super PAC he set up to push forward his political and environmentalist agendas. NextGen Climate Action has been active in organizing its own issue campaigns as well as donating to other liberal groups.

3. George Soros: $7.7 million

George Soros, a business magnate, and a long-time Democratic contributor recently started ramping up his political spending. He dropped a $3 million check in late March to a newly formed super PAC called Win Justice, which has not reported any activities as of yet.

He is the sole contributor to the super PAC so far.

He has also given millions to groups tied to the Democratic Party, including $1 million to the Senate Majority PAC and $380,000 to the American Bridge 21st Century. National Democratic Party committees also received a total of $537,100 from Soros.

George Soros' son, Alexander George Soros, has been following his father's steps to as a big contributor for the Democrats. He recently dropped a $2 million check to the Senate Majority PAC, and also has donated a total of $135,600 to the Democratic National Committee.

4. Donald Sussman: $8.2 million

Hedge-fund manager Donald Sussman, who donated more than $20 million to a pro-Clinton super PAC during the 2016 election cycle, has been a long-time fundraiser and generous benefactor for the Democratic side.

So far this election cycle, the Florida businessman has funneled $6.1 million to more than 150 Democratic campaigns, party committees, and outside groups. He donated $3.2 million to Senate Majority PAC and House Majority PAC, two super PACs with ties to the Democratic leadership in both the upper and the lower chambers.

5. Bernard Marcus: $5.5 million

Home Depot co-founder Bernard Marcus is the biggest financier for the Senate Leadership Fund, a super PAC with ties to Sen. Mitch McConnell, R-Ky. So far this election cycle, he has donated a total of $4 million to the pro-GOP Senate group.

He has been a big contributor for other Republican groups as well, donating $754,600 to the House counterpart Congressional Leadership Fund, $247,700 to Team Ryan and $204,500 to the Republican National Committee, National Republican Congressional Committee, and National Republican Senatorial Committee.

He also donated $300,000 to the John Bolton Super PAC and $250,000 to 35th, Inc., a super PAC that has been supporting Patrick Morrisey in a West Virginia House race.

Home Depot’s political action committee has also donated more than $1.7 million to party committees and candidates, the bulk of that has also gone to Democrats.

6. Fred Eychaner: $4.6 million

Media mogul Fred Eychaner has been exerting his political power mostly through donating to Democratic leadership groups.

He gave $2 million each to the Senate Majority PAC and the House Majority PAC towards the end of last year and has given a total of $474,600 to the Democratic Senatorial Campaign Committee and $237,300 to the Democratic Congressional Campaign Committee.

Some big political names are either far down the list or aren’t even on the list, but that doesn’t necessarily mean that they aren’t invested in the upcoming midterms.

Robert Mercer, who has donated about $3.7 million so far this cycle, has continued to boost his influence through his political group, Club for Growth, which has already reported spending more than $3.1 million this election cycle.

Likewise, the Koch network and its super PAC, Freedom Partners Action Fund, has stockpiled more than $13 million for the upcoming elections, including $3 million from the Charles G. Koch Trust. Americans for Prosperity, another conservative group funded by the Koch brothers, have also spent millions on ads though most of the expenditures have not been reported to the FEC as they don't fall under FEC reporting requirements.

Former White House Deputy Chief of Staff under George W. Bush, Karl Rove, known for his political operations through American Crossroads, has also been funneling more than $15 million to the Congressional Leadership Fund in an effort keep the Republican majority in the lower chamber.

Some other megadonors simply seem to be staying put.

Las Vegas casino mogul Sheldon Adelson, who has donated only about $251,000 with his wife Miriam Adelson so far this election cycle, had poured more than $91 million and $82 million each during the 2012 and 2016 presidential election cycles, but only spent $6 million during the 2014 midterms.

Bloomberg L.P. CEO and former New York City Mayor Michael Bloomberg, who had donated $30 million during the 2014 midterms, has invested only about $508,000 so far this cycle.