LONDON — “Mad” Frankie Fraser, an old-school London criminal who spent more than 40 years in prison and became an underworld celebrity, has died. He was 90.

Eddie Richardson, sometime boss of a crime family with which Fraser was associated, confirmed he died Wednesday. Fraser had been in a hospital for an operation on his leg.

“He’s had a long life and I don’t think he’s done too bad,” Richardson said.

Fraser was among the last survivors of a generation of sharp-suited Cockney gangsters that included the Kray twins, Reggie and Ronnie, who moved between London’s East End dives and the society pages in the 1960s.

Fraser worked as a gangland enforcer for the South London-based Richardsons, and earned a fearsome reputation for violence. He was known as “The Dentist,” for allegedly pulling out his victims’ teeth with pliers.

He served a total of 42 years in prison for a variety of crimes – though never murder – and was sent to psychiatric facilities several times after being declared insane.

After his final release in 1989, he capitalized on nostalgia for the 1960s – even for its shady side – by publishing an autobiography, becoming a television personality, starring in a one-man stage show and leading underworld tours of London.

The world of Fraser and the Krays was mythologized in films such as Guy Ritchie’s “Lock, Stock and Two Smoking Barrels.”

The gangsters became a symbol of a possibly mythical time when criminals only targeted one another, helped the poor and were kind to their sweet old mums.

“Sure I was violent,” Fraser told the Independent newspaper in 1994, “but only to people like myself.”