Bill Richardson was known for many things, the former governor of New Mexico, ambassador to the United Nations and energy secretary under the Clinton administration, but one of his most significant professional achievements was working to free wrongfully detained American citizens abroad.

Richardson died at 75 at his summer home in Chatham, Massachusetts, the Richardson Center for Global Engagement, the organization he founded to promote international peace and dialogue, announced on Saturday.

These are a few of the Americans who Richardson helped to bring home:

Brittney Griner

The two-term Democratic governor and his Richardson Center for Global Engagement organization in New Mexico, worked to secure the release of basketball player Brittney Griner, who was released from a Russian prison in December 2022, after being detained for 10 months. The U.S. swapped the WNBA star for convicted Russian arms dealer Viktor Bout.

The Richardson Center for Global Engagement revealed at the time of her release it had been working with Griner's family and the organization's members had traveled to Moscow several times in efforts to secure her release, engaging with their Russian counterparts and Russian Embassy officials in Washington, D.C.

"Often, the price we pay for bringing our fellow Americans home to their families is unseemly, but it is the right thing to do -- for our fellow Americans, their families, and for our nation," Richardson said in a statement at the time.

Richardson and his organization worked with the White House National Security team on Griner's release, and made efforts to secure the release of Marine veteran Paul Whelan.

"We remain very concerned for Paul Whelan and committed to continue to work on his safe return, as we have been for the last four years," the Richardson Center said at the time of Griner's release.

In a statement to ABC News, Brittany Griner and her wife Cherelle Griner, expressed their condolences over Richardson's passing.

"We were sad to learn of Ambassador Bill Richardson’s passing. Our hearts and prayers go out to his family and friends," the couple said. "We will be forever grateful for all of his efforts to help bring me home from Russia. We applaud his years of tirelessly representing many families of other wrongfully detained Americans."

Trevor Reed

Richardson and his team also worked to secure the release of former Marine Trevor Reed last year, the organization said.

"In this effort, we have had many engagements with our Russian counterparts, and have recently traveled to Moscow, on a private humanitarian mission, to meet with Russian leadership and discuss Trevor’s and Paul Whelan’s release," the Richardson Center said in a statement at the time.

Reed had been imprisoned in Russia for nearly three years, thrown in isolation cells as small as a closet for 23 hours a day, placed in a psychiatric ward and sent to a forced labor camp he described as looking and feeling like something "out of medieval times," he told ABC News.

Danny Fenster

Richardson and the Richardson Center announced in 2021 they helped free American journalist Danny Fenster from a prison in Myanmar.

Fenster had been detained by authorities in Myanmar as he was preparing to board a flight to Kuala Lumpur, Malaysia.

Richardson obtained Fenster's release after face-to-face meetings with Myanmar's Gen. Min Aung Hlaing, the organization said.

"This is the day that you hope will come when you do this work," Richardson said during the announcement. "We are so grateful that Danny will finally be able to reconnect with his loved ones, who have been advocating for him all this time, against immense odds."

Richardson was nominated four times for the Nobel Peace Prize for his work as a diplomat and prisoner negotiator.

ABC News' Patricio Chile, Morgan Winsor, Henderson Hewes, Patrick Reevell, James Hill, and Bill Hutchinson contributed to this report.