British Prime Minister Gordon Brown's rise to power caps a 24-year career in politics - much of it spent alongside his friend and rival Tony Blair.
Like his predecessor, Mr. Brown began his political career in 1983, winning a seat in parliament for the Labor Party. He worked his way up the party leadership ladder over the next decade.
He was named finance minister in 1997 following the Labor Party's election win, and held that post until Wednesday.
Mr. Brown, a 56-year-old Scot, is widely credited with spurring a decade of British economic growth. He is well known for his decision to give Britain's central bank, the Bank of England, the financial independence to fight inflation. He also kept Britain out of the single European currency, the Euro.
Mr. Brown has vowed to revitalize the ruling Labor Party.
He has also acknowledged that mistakes were made in the Iraq war, although he has been broadly supportive of Britain's military actions in both Iraq and Afghanistan.
It has been widely reported that Mr. Blair and Mr. Brown struck a deal in 1994 under which Mr. Brown agreed not to run against Mr. Blair for the post of party chief after the death of then-party leader John Smith.
In return, Mr. Blair is said to have agreed to grant Mr. Brown broad powers as treasury chief, while promising to step down before his second term expired - which never happened.
Mr. Brown attended Edinburgh University, where he earned a first-class degree and a doctorate. He married public relations executive Sarah Macaulay in 2000. The couple has two sons.
Some information for this report was provided by AFP, AP and Reuters.