President-elect Donald Trump appointed Stephen Miller to be his senior adviser for policy, the latest move to fill out his White House inner circle ahead of the inauguration.

Miller, a former Senate aide to Attorney General-designee Jeff Sessions, joined Trump in January as the campaign’s senior adviser for policy, a role he continues to play for the transition. Miller became a familiar face on the campaign trail by introducing Trump at rallies. He is one of Trump’s youngest senior staffers.

“Stephen played a central and wide-ranging role in our primary and general election campaign,” Trump said in a statement. “He is deeply committed to the America First agenda, and understands the policies and actions necessary to put that agenda into effect.”

Miller began his career as a spokesman for lawmakers including Rep. Michele Bachmann (R-Minn.) and John Shadegg (R-Ariz.) before joining Sessions’s staff in 2009. He joined the Trump campaign after helping Trump’s team craft its immigration policy at Sessions’s request.

Trump named two other members of his White House leadership team on Nov. 13: Stephen K. Bannon as chief strategist and senior counselor to the president, and Republican National Committee Chairman Reince Priebus as White House chief of staff.

In a statement, Miller said he was “deeply honored” by the opportunity to join Trump’s White House. His role includes the title of assistant to the president.