The incoming Russian ambassador to the U.S. is "formidable," "tough," and a "skilled negotiator," according to an American ex-diplomat who has sat across the table from him.

Anatoly Antonov, Russia's former deputy defense minister and deputy foreign minister, is set to take on the role of Ambassador to the U.S. on Sept. 1, according to a Russian media report, replacing longtime diplomat Sergey Kislyak. In June, reports surfaced that Kislyak was being recalled to Russia, after he became a recurring character in the drama surrounding the Trump administration's contacts with Russian officials.

Longtime former U.S. State Department official Amb. Laura Kennedy, who dealt with Antonov years ago before he joined the defense ministry, provided the "formidable" description of Antonov in tweets today.

"I knew incoming Russian Amb to US Antonov... when he headed MFA [Ministry of Foreign Affairs] arms control - a formidable diplomat," she wrote. "Formidable meant tough, skilled negotiator e.g. NewSTART/NPT [arms treaties]. This was before he became [Deputy Defense Minister] where his Ukraine work got him sanctioned by EU."

As Kennedy mentioned, in February 2015, Antonov was the highest-ranking Russian among those targeted by the European Union for sanctions in response to the Russian invasion of Ukraine.

“He was a very outspoken defender of the whole thing, very nasty in his attacks,” former U.S. ambassador Alexander Vershbow told Politico last month. “You can expect to hear him talking a lot about NATO encirclement of Russia... He not only says that stuff but he believes it.”

Profiles of Antonov in Politco,  The Daily Beast and NPR suggest he'll bring a harder edge to diplomacy in America than Kislyak did.

“Considering the current tensions in U.S.-Russia relations, Moscow wanted to bring a tough character to Washington," Igor Bunin, the director of Moscow-based Center for Political Technologies, told The Daily Beast in late June.

A biography of Antonov posted on the Russian Foreign Ministry's website says he was born in 1955, graduated from Moscow State Institute of International Relations, earned a PhD in Political Science and is fluent in English and Burmese.