Vitaly Churkin, the Russian ambassador to the United Nations, died suddenly on Monday in New York City, one day before his 65th birthday.

According to the New York Post, Churkin was at the Russian embassy on East 67th Street on Monday morning, when he suffered a “cardiac condition.”  He was then rushed to the New York Presbyterian Hospital at around 9:30 a.m, where he arrived unconscious and in need of CPR.

Churkin was considered a tough talker, frequently defending seemingly indefensible positions taken by the Kremlin on the world’s stage at the United Nations.  He served as Russia’s envoy to the global organization since 2006, where he established a reputation for being intelligent and capable, frequently standing toe to toe with representatives from Russia’s political opponents like the United States.  Prior to his death, Churkin was the longest-serving member of the U.N. Security Council, which is recognized as the most powerful body within the organization.

“We did not always see things the same way, but he unquestionably advocated his country’s positions with great skill,” Nikki Haley, the American ambassador to the United Nations, said in a statement. “We send our prayers and heartfelt condolences to lift up his family and to the Russian people.”