LONDON - After a decade of waiting on the sidelines, Gordon Brown is about to get his big break.

The taciturn treasurer, credited for much of Britain's recent economic boom, is almost certain to become the next prime minister by the end of June, when Tony Blair steps down.

Often described as dour, Brown, 56, has been criticized for everything from his dandruff to his alleged "Stalinist ruthlessness."

But he is largely an enigma, with little known about his political leanings.

He has close ties to Democrats in the United States and is said to be particularly close to Massachusetts Sen. John Kerry.

"I don't think we'll see true Brown until the general elections," said Anthony Seldon, a biographer who has followed both Blair and Brown.

General elections are not expected before 2009, which will spark a vicious fight between Brown, a rumpled intellectual, and David Cameron, the fresh-faced leader of the Conservatives who has been compared to the younger charismatic Blair.

Brown once promised to "spend what it takes" to disarm Saddam Hussein and is likely to keep British troops in Iraq for the near future. He also will probably try to maintain a strong relationship with Washington.

Former Cabinet Minister Charles Clarke called Brown a "control freak" last year. Andrew Turnbull, the former head of Britain's civil service who broke a customary code of silence, said Brown had often belittled his colleagues.

Brown and Blair won their Parliament seats in 1983. It was the start of a long and often bitter rivalry for the pair known as the "Odd Couple."

The two found themselves sharing an office in Westminster. Immediately, they spotted each other's strengths.

When Labor Party leader John Smith died of a heart attack in 1994, both men were considered for the job.

Political lore has it that the men, while dining at a trendy London restaurant, struck a deal stipulating that Blair would take over as party leader on the condition that Brown would get control of the Treasury. Blair was then to step down halfway through his second term to make way for Brown as prime minister.

That never happened.

Brown's days in waiting were immortalized in The Queen, last year's film that focused on Blair and Britain's royal family in the aftermath of the death of Princess Diana. In one scene, Blair is in a meeting when an aide rushes in and announces, "Brown is on the telephone."

"Tell him to wait," Blair says.

British newspapers have been saturated with rumors of squabbles between the two.

While Blair initially supported the notion that Britain could embrace a common European currency, Brown shot down the idea, establishing a multifaceted test to show that the British economy would surely suffer. Blair, needing Brown's backing, quickly dropped the notion.

Few could ignore Brown's economic mastery or political ambition. He started canvassing for Labor at age 12 and graduated from Edinburgh University in Scotland with a doctorate. His thesis was on the links between Labor and Scottish trade unions, according to Robert Peston, author of the 2005 book Brown's Britain.

Brown stuck to Labor's 1997 pledge to freeze income taxes. He increased government expenditures.

Tragedies have been part of Brown's life.

His daughter, Jennifer Jane, was born premature in 2001 and died of a brain hemorrhage days later. His son Fraser, born in July, was diagnosed with cystic fibrosis. He and his wife, Sarah, have another son, John, 3.