Kevin Weeks (born March 21, 1956) is an American former mobster and longtime friend and mob lieutenant to Whitey Bulger, the infamous boss of the Winter Hill Gang in South Boston, a crime family formerly based in the Winter Hill neighborhood of Somerville, Massachusetts.

After his arrest and imprisonment in 1999, he became a cooperating witness. His testimony is viewed as responsible for the convictions of FBI agent John Connolly, as well as forcing Bulger's right-hand man, Stephen Flemmi, to plead guilty as well. Since his release from prison, he has written the true-crime memoir, Brutal: My Life in Whitey Bulger's Irish Mob. This was followed by Where's Whitey?, a novel using Bulger as a character, co-written with Phyllis Karas. Promotion for the book started on the day the FBI stepped up its efforts to catch Bulger with an advertisement; Bulger was caught two days later.

Kevin Weeks was born in South Boston, Massachusetts, on March 21, 1956, to a working-class family of Irish and Welsh descent. He was the fifth child in a family of six and grew up in the Old Colony Housing Project at 8 Pilsudski Way, apartment 554. His father, John Weeks Sr., originally hailed from Brooklyn, New York. He changed tires for a living and later obtained a position with the Boston Housing Authority.

Weeks had two brothers, William and John Jr., and three sisters, Maureen, Patricia, and Karen. John Sr. trained his sons in boxing and earned extra money by coaching prizefighters. Kevin first started attending school at Michael J. Perkins, but then changed to John Andrew School in Andrew Square for grades 5 and 6; he finally completed elementary school at Patrick F. Gavin School. He graduated from South Boston High in 1974, ending his formal education. His two brothers graduated from Harvard University and would seek out careers in politics: John Jr. became an advance man for Massachusetts Governor Michael Dukakis, and William became a selectman in Acton, Massachusetts.

Kevin's brother, William, has described their childhood: "Smart was good, but having the ability to beat someone senseless! Now that was real power. Education was often talked about in the apartment, but always with the implied threat that if your marks weren't acceptable, be ready to give up your soul to God because your ass belonged to our father ... and As weren't acceptable."

In 1975, Weeks became a bouncer at a popular neighborhood bar called Triple O's Lounge, owned by Kevin O'Neil. This was a frequent hangout of the Winter Hill Gang, an Irish-American crime family which was then headed by James J. "Whitey" Bulger. It was here that Weeks first met Bulger, as well as Bulger's Italian-American partner Stephen "The Rifleman" Flemmi.

Beginning in 1978, Weeks began working for Bulger part-time as muscle and a personal driver. Impressed by Weeks' knack for making money and genuinely liking him, Bulger decided to bring him in closer than any other associate. Meanwhile, Weeks turned to running a loansharking business on the side.

In 1982, four years after beginning to work as part of the Winter Hill Gang, Weeks left his legitimate job and became a full-time mobster in the gang.