A small-to-mid-time gangster in London during the 1950s and 60s, Jack the Hat was famously murdered by the Kray Twins--one of only two crimes of which they were convicted (the other being the murder of George Cornel).
His life appears to have been otherwise quite unremarkable--a little robbery here, some drug dealing there (Black Bombers being his personal pill of choice). Jack appears to have enjoyed his fighting and, although he was a big, tough man, was often on the receiving end of some fierce baeatings. According to some, Jack's trademark hats represent a none-too-subtle attempt to draw attention from the increasingly bald state of his pate.
Jack was never a member of the Kray's "Firm". His gruesome end was precipitated when he failed to carry out the murder of one of the Kray’s associates, Leslie Payne, whom Ronnie Kray thought was going to turn Queen’s evidence. Not only did McVitie take Ronnie’s money, in the autumn of 1967, his drunken and aggressive behavior in bars owned by friends of the Krays angered the brothers to the extent that they decided to personally remove him from the scene. They had him lured to a house on the pretext of a party and Reggie Kray killed him in the most brutal fashion.
Jack the Hat's final days have been fictionalized by Jake Arnott in his novel "The Long Firm".
Thanks to http://www.crimelibrary.com/gangsters_outlaws/mob_bosses/kray/removal_12.html?sect=15 and following pages