Khizr Khan was on the undercard of a Democratic National Convention schedule on Thursday that included the keynote address by Hillary Clinton, but instead, the father of a Muslim soldier killed in Iraq ended up stealing the spotlight with an emotional address that tore into Republican candidate Donald Trump.

The speech had many turning to the internet to learn more about Khan, who has been stepping into the national spotlight in recent months to share his thoughts on the Republican nominee and on the duty of Muslims to root out extremists in their midst.

A longtime critic of Trump, Khan used the spotlight of the final night of the DNC to slam Trump for his proposal to ban non-American Muslims from entering the country. While praising his son’s own sacrifice in Iraq and sharing the hopes and dreams his son had for the future, Khizr noted that the family would have never been able to enter the United States if it were up to Trump.

“Like many immigrants, we came to this country empty-handed. We believed in American democracy — that with hard work and the goodness of this country, we could share in and contribute to its blessings,” Khan said.

Khizr Khan then delivered one of the most memorable moments of the entire night, pulling a copy of the U.S. Constitution from his pocket and asking Trump if he had ever read it.

Khizr’s son, Captain Humayun S. M. Khan, was killed on June 8, 2004, in an attack north of Baghdad. The 27-year-old Humayun was inspecting soldiers on guard duty at a compound when an attacker drove a vehicle packed with explosives into the gate, Arlington National Cemetery’s website noted. Khan was one of 14 American Muslims killed in action during the decade that followed the September 11 terrorist attacks.

As Khizr Khan told Vocativ last year, his son’s selfless actions before being killed actually saved a number of other soldiers.

“As soldiers under Khan’s command prepared to inspect the vehicle, his father told us, Captain Khan screamed for his men to ‘hit the dirt’ and walked towards it himself and demanded the driver stop. Inside the car were two suicide bombers and a large amount of explosives. As the car reached the gate, the bomb was detonated, killing Khan and wounding 10 U.S. soldiers. His father believes many more men might have died without Khan’s warning. Khan was posthumously awarded the Bronze Star and the Purple Heart, two of the military’s highest honors.”

In his speech on Thursday, Khizr Khan also shared his son’s dream of becoming a military lawyer, one that was cut tragically short by the attack in Baquabah.

Khizr Khan’s speech seemed to have an immediate impact. Wired reporter Nate Goldman noted that immediately after his speech concluded, searches for “register to vote” saw a dramatic rise on Twitter.

As soon as Khizr Khan finished his speech, "register to vote" spiked as a Google search. pic.twitter.com/0HZbBuCWwR — Nate Goldman (@NateGoldman) July 29, 2016

Khizr Khan has actually been a critic of Donald Trump dating back even before the first primary of this election season. In his December, 2015, interview with Vocativ, Khizr said he was proud of his family and proud of the sacrifices many other Muslim immigrants have made to make America better.

“We are proud citizens,” he said.

Khizr Khan has also been a vocal critic of Muslim terrorists, saying that moderate Muslims have a duty to root out extremists in their midst.

“This is the time for us American Muslims to rat out any traitor who walks amongst us. This is high time for Muslims to stand firm [against terrorists],” he said. “Among us hides the enemies of the value system of this country. And we need to defend it. And if it means ratting out the traitors who hide behind an American passport, that’s what we need to do.”

The speech delivered by Khizr Khan was an immediate hit, with Khan’s name appearing as a top trending term on Twitter and video of the speech quickly racking up views on YouTube.

[Photo by J. Scott Applewhite/AP Images]