Bill Richardson, U.S. presidential hopeful in 2018 and a two-term governor of New Mexico, has passed on at 75.

The former governor died “peacefully” in his sleep at his residence in Chatham, Massachusetts, a statement by Richardson Center for Global Engagement said.

“Governor Richardson passed away peacefully in his sleep last night,” Mickey Bergman, vice president of the Richardson foundation, said in a statement.

Mr Richardson had previously worked as a U.S. ambassador to the United Nations and was known for working assiduously to secure the freedom of American citizens wrongfully detained in other countries. He was passionate about human rights advocacy that then-President Bill Clinton nicknamed him “undersecretary for thugs.”

“He lived his entire life in the service of others — including both his time in government and his subsequent career helping to free people held hostage or wrongfully detained abroad,” mourned Mr Bergman. “There was no person that Governor Richardson would not speak with if it held the promise of returning a person to freedom. The world has lost a champion for those held unjustly abroad, and I have lost a mentor and a dear friend.”

Tributes and encomiums have already begun to pour in from political juggernauts familiar with Mr Richardson’s advocacy for the wrongfully detained.

“I mourn the passing of this New Mexico legend, one of the most powerful Hispanics in politics that this nation has seen,” Gabe Vasquez, U.S. representative for New Mexico, wrote on X. “Today, we reflect on his decades of service and for always proudly representing New Mexico.”