The school's board of trustees immediately voted to accept the resignation, which is effective Sept. 1.

The departure came just two months after UMass trustees expressed confidence in Bulger even as a storm of protest swirled around him and his testimony before a congressional committee investigating the FBI's ties to its mob informants.

He testified under immunity before the panel in June about his mob brother, James "Whitey" Bulger, who has been on the lam since 1995. Whitey Bulger fled just before his indictment on federal charges related to 21 murders.

While admitting he had spoken to his brother once since he fled, Bulger said he has no idea of his whereabouts and said there is little he could have done to steer him from a life of crime. Whitey Bulger is now on the FBI's "10 Most Wanted" list.

William Bulger also said he thought the FBI investigators were trying to get his brother killed when they leaked to the media the fact that Whitey Bulger had been an informant.

Bulger's critics said his testimony was evasive and questioned how he could be so ignorant of his brother's criminal activities.

Bulger is a legendary political figure in Massachusetts, where he carved out a reputation as a powerful force during his unprecedented 17 years as the president of the state Senate.

Part of the intrigue surrounding Bulger is centered on his relationship with his mobster brother -- how the two men emerged from a poor South Boston background and ended up on different paths in adulthood.

During his appearance before the congressional committee, Bulger talked publicly for the first time about the brief telephone conversation he had with his brother after he fled. But he said they never discussed whether Whitey Bulger should turn himself in, and he never advised his mobster brother to stay away.

"It was a conversation of about three or four minutes duration," Bulger said. "The tone of it was 'Don't believe everything that is being said about me' ... I think he asked me to tell everybody he was OK ... I think I said I hope this has a happy ending."

In the past year, pressure has mounted against Bulger from a variety of political quarters. Republican Gov. Mitt Romney has urged Bulger to resign -- as did the state's highest-elected Democrat, Attorney General Thomas Reilly.

Both said the controversy had distracted the school from its educational mission.

"Having the governor and attorney general pitted against you, certainly isn't going to help the university going forward," said trustee Lawrence Boyle, who had publicly called for Bulger to step down. "I don't see that the storm clouds are ever going to lift over the university when he's there.

"His departure, I think, is going to abate all this ancillary discussion about grand juries and death pits and let us focus back on books and scholarships," Boyle said.

Bulger, who became UMass president in 1996, was paid $309,000 in salary and another $48,000 in benefits. He contract was set to expire in 2007.