JAKE Sullivan, who is just 43, is expected to be named Joe Biden's national security adviser.
President-elect Biden will move into the White House on January 20 after capturing the November 3 election.
Who is Jake Sullivan?
Sullivan is a senior policy adviser for Biden and is expected to become the national security adviser to the 46th president of the US.
He served in the Obama administration and has also taught at Yale Law School, Dartmouth College, and the University of New Hampshire.
"During his time in government, Sullivan was a lead negotiator in the initial talks that paved the way for the Iran nuclear deal and played a key role in the US-brokered negotiations that led to a ceasefire in Gaza in 2012," reads his Biden-Harris transition bio.
"He also played a key role in shaping the Asia-Pacific rebalance strategy at both the State Department and the White House."
He graduated from Yale and was a Rhodes Scholar at Oxford.
Sullivan, who will turn 44 on November 28, lives with his wife Maggie Goodlander in Portsmouth, New Hampshire.
What did Sullivan say about his appointment?
Sullivan tweeted on November 23 that Biden "taught me what it takes to safeguard our national security at the highest levels of our government."
"Now, he has asked me to serve as his National Security Advisor.
"In service, I will do everything in my power to keep our country safe."
Who has Biden picked for his administration?
Biden has announced picks for multiple Cabinet-level positions ahead of his January 20 inauguration.
The formal announcement on Biden filling out his administration came on Monday after the nominations began to trickle out to the news media.
Biden confirmed that he is going to nominate Antony Blinken for secretary of state.
Blinken served as deputy secretary of state and deputy national security adviser in the Obama administration.
Biden has also picked nominees for Homeland Security, United Nations ambassador, treasury secretary, special presidential envoy for climate change, director of national intelligence, and national security adviser.
John Kerry - a Vietnam War vet, former secretary of state, and senator who ran for president in 2004 and lost to George W Bush - has been nominated to lead the Biden administration's climate change effort.
Former Federal Reserve Chair Janet Yellen is expected to run the Treasury Department.
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Alejandro Mayorkas will be nominated as the secretary for the Homeland Security – the first-ever Latino and immigrant to serve as secretary.
Biden has chosen Avril Haines to serve as the director of national intelligence, and Linda Thomas-Greenfield, as the US ambassador to the United Nations.
Haines served as the deputy CIA director from 2013 to 2017, and was the first woman to hold that office - and is the first woman nominated to lead the intelligence community.