Wendy Sherman, a deputy to US Secretary of State Anthony Blinken, announced on Friday that she will retire at the end of June after three decades in Washington’s Foreign Service, Reuters reports.

Wendy Sherman is the first woman to hold her current post, a position from which she oversaw the Biden administration’s diplomatic relations with China and engaged in dialogue with Russia in an effort to prevent the February 2022 invasion of Ukraine.

Secretary of State Anthony Blinken has expressed his appreciation for the work being done by Wendy Sherman, whose diplomatic skills over the years have earned her the nickname The Silver Fox. Blinken noted that Sherman broke some barriers as a woman in diplomacy and worked on “some of the most difficult foreign policy challenges of our time.”

“Thanks to her leadership, our nation is safer and more secure, and our partnerships are stronger,” Blinken said in a statement.

In a memo to State Department staff announcing his resignation, Sherman said his final term in government, beginning in 2021, has been marked by geopolitical changes, citing the U.S. withdrawal from Afghanistan, increased competition with China and the war in Ukraine.

“Nothing was open to direct answers,” Sherman wrote in a memo seen by Reuters.

In January 2022, as Russian troops massed near Ukraine’s borders, Sherman was sent to meet with Russian Deputy Foreign Minister Sergei Ryabkov in Geneva, but talks broke down as Moscow insisted on security terms that Washington had already rejected as unsustainable. Among them was the withdrawal of NATO forces and equipment to the formation before the expansion of the alliance into the former communist space in Europe.