Democratic congressman Elijah Cummings, a prominent civil rights activist, chairman of the House Committee on Oversight and Reform and key figure in President Donald Trump’s impeachment inquiry, died on Thursday from “complications concerning longstanding health challenges,” according to a statement issued by his office. He was 68.

Cummings has been a representative of Maryland’s 7th Congressional District since 1996. During his time in the House of Delegates, he was the first African American from Maryland to be named Speaker Pro Tem and the youngest chairman of the Legislative Black Caucus.

In addition to his work investigating the impeachment inquiry, Cummings has also been a vocal advocate for children and families detained at the U.S.-Mexico border. His committee was heavily involved in the Michael Cohen hearing in February.

His scrutiny of Trump extended to the president’s family as the congressman led probes on his family members serving in the White House.

Cummings was Hillary Clinton’s chief defender in the 2015 Benghazi hearings. That same year, he marched in Baltimore in solidarity with the community after the death of 25-year-old Freddie Gray, who died while in police custody. He was also the co-chairman of Barack Obama’s Maryland campaign in 2008.

A native of Baltimore and the son of sharecroppers, Cummings graduated from Howard University, with a bachelor’s degree in political science, and the University of Maryland School of Law. After earning his law degree, he joined a firm in Baltimore until he started his own practice. In 1982, he won the state delegate position, where he served for 14 years. In 1995, he ran for congressman in the 7th congressional district for Maryland and won.

“He spoke truth to power, defended the disenfranchised and represented West Baltimore with strength and dignity,” tweeted Rep. Hakeem Jeffries, House Democratic caucus chairman and a fellow member of the Congressional Black Caucus, on Thursday. “Congress has lost a Champion. Heaven has gained an Angel of Justice. May he forever #RestInPower.”

Trump sent his “warmest condolences” in a tweet on Thursday morning.

Other politicians, including the Obamas, and Hollywood figures mourned Cummings’ loss as well.