Allan Williams played an important role in the Beatles' early career as an agent and a manager of sorts. Not nearly as important a role as he sometimes claimed, but an important one nonetheless, in helping them navigate the transition from amateur to professional band. Williams was a club owner in Liverpool, operating the Jacaranda coffee bar, where he had met John Lennon, Stuart Sutcliffe, and other students from the nearby Liverpool Art College. Williams was starting to get involved in music promotion by helping stage rock shows, particularly a 1960 concert by Gene Vincent, and aiding local Liverpool bands. In this way he came into contact with leading early British rock manager Larry Parnes (who handled Billy Fury, Marty Wilde, Vince Eager, Duffy Power, and so on). Parnes wanted to use Liverpool musicians to back his solo acts, and held auditions in Liverpool in which the Beatles secured a slot on a brief Scottish tour backing one of Parnes' more obscure clients, Johnny Gentle.
Through a fantastic but apparently true whirlwind of events in 1960, Allan Williams found himself a key figure in securing engagements for British bands in Hamburg, Germany, and thus became a key figure in developing British rock as a whole. A Caribbean steel band that played at his club left Williams to take an offer in Hamburg. Based on their reports of Hamburg's thriving club scene, Williams made contact with Hamburg club owner Bruno Koschmider, and started to send Liverpool rock bands to Hamburg, acting as their agent. The Beatles were not the first band he sent; they were not regarded as a good group at the time, and they were preceded by the little-known Derry & the Seniors. When Koschmider wanted more bands, Williams' first choices were Rory Storm & the Hurricanes (whose drummer was Ringo Starr) and Gerry & the Pacemakers. When they were unavailable or unwilling, however, the Beatles got their chance, securing a drummer, Pete Best, only days before leaving. Williams had already gotten the Beatles some work in Liverpool by enlisting them as the backup band for a stripper for a week.
As that anecdote shows, Williams was a small-time hustler. But what he did manage to do for the Beatles, in his bumbling fashion, shouldn't be underestimated. He even drove them to Hamburg in August 1960 in his van for their first engagement at Bruno Koschmider's Kaiserkeller. By continuing to help send Liverpool bands to Hamburg, Williams, perhaps unwittingly, gave them the opportunity to sharpen their acts in arduous sets in front of raucous, demanding audiences, and thus helped spark the British Invasion sound.
It would not be strictly accurate to call Williams the Beatles' manager. He did help them get some other bookings besides the first (multi-month) Hamburg engagement, but the Beatles also worked with other promoters and informal advisers at the time. The relationship between Williams and the Beatles was permanently ruptured when the group went back to Hamburg in early 1961 for a second extended engagement. Having felt that they themselves had negotiated this contract, they (Stuart Sutcliffe, actually) wrote Williams to inform him that they would not pay him a commission. Although Williams threatened to contest this, he never did, and things cooled off enough eventually that they resumed amiable, unprofessional relations. Williams was embittered enough by their behavior, though, to tell Brian Epstein not to "touch 'em with a f*cking bargepole" when Epstein sought his advice on whether to manage the Beatles.
Epstein, of course -- a well-to-do businessman who already had contacts in the music industry via his administration of one of the most prosperous record retailing outlets in Northern England -- was able to do far more for the Beatles than Williams ever could have. Williams did continue to be involved with rock music and the entertainment scene, in general, over the next few years with his club the Blue Angel. (A previous endeavor, the Top Ten Club -- envisioned as a counterpart to the rock club of the same name in Hamburg -- had burned down only days after opening in December 1960.) Although he already had contacts with many of Liverpool's bands, Williams was too disorganized, and lacked the resources, to effectively capitalize on this, and did not emerge as a significant manager and promoter as the British Invasion became a phenomenon.
Williams' role in the Beatles story was not wholly finished after 1961. In the early '70s, he and Ted Taylor, leader of Liverpool band Kingsize Taylor & the Dominoes, retrieved live tapes of the Beatles performing at Hamburg's Star-Club in December 1962 from an abandoned studio. For the next few years Williams actively lobbied for their release, even meeting with George Harrison in an attempt to convince him. These finally came out in 1977 (by which time Williams had sold his official interest in the project), although their legality has been contested on and off since then. Williams also published his autobiography (The Man Who Gave the Beatles Away, co-written by Bill Marshall) around this time, in which the Beatles figure prominently, as do some other Liverpool groups. It has since been written, however, that much of the material in the book was based only loosely on real events.