The 45-year-old Ahern is the youngest Taoiseach (Gaelic for prime minister) Ireland has had, and was described once by his mentor, Charles Haughey, as "the best, the most skillful, the most devious and the most cunning."
Brought up in a working class Dublin suburb, Ahern is the son of a man who fought with the IRA in the war of independence and then became a staunch member of the party Ahern now leads, Fianna Fail (Soldiers of Destiny). His mother was also from a Republican family in Cork and ran his constituency office for many years. Older brother, Noel, is a member of parliament.
Trained as an accountant at University College in Dublin, Ahern is said to keep his eye on the bottom line. "Form before function is how he approaches everything," says a former colleague.
A political commentator says Ahern is affable, practical and well-liked, "although people aren't sure of his competence" when it comes to the economy.
Although neither an intellectual nor a great speaker, and hardly an inspirational figure, he has in his own resolute way broken new ground in Ireland: Ahern is the first Taoiseach to separate from his wife and openly carry on a relationship with another woman.
A Catholic, Ahern enjoys attending football matches with his daughters and prefers Bass Ale to the local brew, Guinness -- but gives it up each year during Lent.