In the years following Whitey's release, William blamed the press for spreading what he called "lurid allegations" about his brother, speculating that some of the "dark rumors" were nothing more than political attacks on him.
As Whitey's criminal activities allegedly turned more brutal, William Bulger rose through the Statehouse ranks. In 1970 he won a Senate seat and eight years later was elected Senate president by the 40-member chamber, a position he would hold for a record 17 years.
Even after Whitey fled in 1995 of the eve of his indictment on racketeering charges, William remained loyal, accusing overzealous prosecutors of buying testimony with promises of early release from prison.
"It has been known for many years that a 'get out of jail' card has been available to anyone who would give testimony against my brother," he wrote.
At the same time, William was earning a reputation as a tough-minded leader who rewarded supporters and punished critics.
Warren Tolman, a former Democratic senator who was among those critics, served briefly under him.
Tolman said that although he often found himself at loggerheads with William Bulger, he felt Bulger treated him fairly and could be "a charming guy" when he wanted.
Still, Bulger wasn't shy about using his political might.
Tolman said after he was able to prevent a transportation funding proposal from passing by a single vote, Bulger, who opposed the measure, used his muscle to flip a vote, forcing the proposal through.
"By and large he got his way whenever he wanted," Tolman said. "You knew that if you took him on it was going to be an uphill battle."
Tolman said he never recalled open discussions about Bulger's brother even his Senate colleagues "certainly knew of the legend of Whitey Bulger."
"I don't think anyone ever realized the scope of the dastardly deeds he's accused of," Tolman said.
Occasionally the lines between politics and the underworld blurred.
In 1994, then-state Sen. William Keating led a group of like-minded liberal lawmakers in an attempt to oust Bulger as Senate president.
Although the challenge failed, the campaign against Keating was fierce. Keating said his supporters from South Boston told him that Whitey had paid people to travel to Keating's district to hold signs for his Republican opponent.
Keating said he had his own brief run-in with the reputed mobster, who approached him and lit into him with a barrage of profanity-laced insults for trying to take down his brother.
Keating, who went on to become Norfolk District Attorney before being elected to Congress last year, said he's friends with a family who lost a loved one to Whitey's violence, according to the indictments against him.
"There's a tendency to glamorize abuse of power and a tendency to glamorize the gangster life, but as a district attorney I was there as they were unearthing the bodies of (Whitey Bulger's) victims," Keating said. "It's not funny and it's not glamorous. It was savage and it was brutal."
In a written statement following Whitey's arrest this week, William Bulger said he wished to "express my sympathy to all the families hurt by the calamitous circumstances of this case."
Then, during Whitey's brief appearance in federal court in Boston on Friday, the aging brothers had a fleeting reunion of sorts. Whitey, now 81, smiled at his younger brother and mouthed the word 'Hi.' William smiled back.
William, speaking briefly to reporters as he left the courthouse, appeared emotional.
"It's an unusual experience," he said.
- Hillary Clinton selects running mate for...
- AP Poll: Support grows among Americans for...
- IS attack on Afghan protest kills 80 people,...
- Political scandals linger as Philly readies...
- How Hillary Clinton chose Virginia Sen. Tim...
- Police say Munich suspect was obsessed with...
- AP PHOTOS: A selection of pictures from the...
- Hillary Clinton still hard to define despite...
- Sarah Silverman: Bernie-or-bust Dems... 49
- Is Bernie Sanders an atheist? 42
- Clinton wins historic nomination,... 36
- After turmoil, Sanders, Michelle Obama,... 31
- Dems' division, emails roil party on... 28
- Trump says Russia should find Clinton's... 27
- Watch live at the Democratic National... 25
- In wake of email hack, Democratic chair... 23