Howie Winter, the longtime leader of Somerville’s notorious Winter Hill Gang and a former crime partner of James “Whitey” Bulger’s, died Thursday of a heart attack at his home in Millbury, according to his lawyer. . He was 91.

Winter’s death, he said, is “the true end of an era.”

During testimony in Bulger’s 2013 trial, Winter was implicated in a number of murders from the Irish gang wars of the 1960s and 1970s, including a young bartender who worked at a North End restaurant and was gunned down in 1973 in a case of mistaken identity. Winter was never charged with any of them, although he served time for fixing horse races at six East Coast race tracks, and drug trafficking.

“It’s the end of a legend, but not a good legend,” said Thomas Foley, a retired Massachusetts State Police colonel who investigated organized crime for decades. “He is a guy that actually got away with murder.”

The Somerville gangster was a throwback to a time when Boston’s dominant organized crime groups were the Mafia and the Winter Hill Gang — the so-called Irish mob, which was actually an amalgamation of Irish and Italian gangsters. The two groups controlled bookmaking and loansharking throughout the region, and though competitive, respected each other’s territory.

“The Mafia feared him,” Foley said of Winter. “They felt it was better to have a working relationship with him than take him on.”

Winter’s longtime friend, James Martorano, a former Winter Hill Gang associate, said Winter was blamed for many things he didn’t do, and had also done a lot of good for people. “We all loved him,” he said. “It’s a big loss for us.”