William Michael Bulger (born February 2, 1934) is an American former Democratic politician, lawyer, and educator from South Boston, Massachusetts. His eighteen-year tenure as President of the Massachusetts Senate is the longest in history. After leaving office, he became president of the University of Massachusetts.

Bulger came from Old Harbor Village Housing Development (now more commonly known as the Mary Ellen McCormick Housing Development). He graduated from Boston College High School in 1952, then from Boston College in Classics, then from Boston College Law School.

Bulger was the younger brother of the convicted mob boss James "Whitey" Bulger, who led the Winter Hill Gang, and he received harsh criticism for refusing to distance himself from his brother, who was convicted of participating in 11 murders and sentenced to life in prison, or to cooperate with authorities after he became a fugitive. He was forced to resign from the presidency of the University of Massachusetts. Bulger went on to teach as a visiting scholar at Suffolk University, but has since removed himself from public life.

William Bulger's father, James Joseph Bulger Sr., was from Harbour Grace, Newfoundland. After settling in Everett, Massachusetts, James Sr. married Jane Veronica "Jean" McCarthy, a first-generation Irish immigrant. William Bulger was born in Dorchester, Massachusetts, and is the third of six children in the family, and younger brother of former mob boss James Joseph "Whitey" Bulger Jr. (1929–2018).

Bulger's father worked as a union laborer and occasional longshoreman; he lost his arm in an industrial accident and the family was reduced to poverty. In May 1938, when Bulger was four years old, the family moved to South Boston's Old Harbor Village housing project, soon after it opened. He grew up there and has maintained lifelong friendships with many of those who were his former neighbors, including best friend, Korean War Marine P.O.W. and Purple Heart recipient Fred L. Toomey. The late Congressman Joe Moakley (1927–2001) was also a close childhood neighbor. Although the Bulger family was poor, William matriculated into Boston College High School. He enrolled at Boston College in 1952, but his undergraduate career was interrupted when he joined the United States Army. He served from September 1953 to November 1955, then returned to Boston College, completing his undergraduate degree in English Literature with the help of the G.I. Bill. He attended Boston College Law School, from which he received his Doctor of Jurisprudence degree in 1961. He is also the recipient of over 20 honorary degrees from a variety of academic institutions.

Bulger became interested in politics in 1959 and was first elected to the Massachusetts House of Representatives as a Democrat in 1960. After serving five terms, Bulger was elected to the Massachusetts State Senate in 1970 representing the First Suffolk District. In 1973, he was named Second Assistant Floor Majority Leader. After Joseph DiCarlo's conviction for extortion in 1977, Bulger succeeded him as Senate Majority Leader. Bulger was elected President of the Massachusetts State Senate in 1978 and was re-elected every two years through 1996, making his time as State Senate president the longest tenure in Massachusetts history.

Like other Massachusetts politicians who were elected leaders of their legislative chambers, Bulger was frequently pilloried in the media, but remained very popular in his district. He won his district election every two years from 1961 to 1994 without ever facing a serious challenger other than in the Democratic primary in 1988, when Stephen Holt, a neophyte liberal activist and bookstore owner from Dorchester, won 31 out of 60 precincts, only to lose by a landslide due to the huge turnout of Bulger supporters in South Boston.

Bulger appeared in Primary Motive as Senator William Bulger.