In classic Hollywood fashion Guy McElwaine rose from the mail room at Paramount Pictures in the 1950s to become head of Columbia Pictures in the 1980s, overseeing such classics as Gandhi (1982) and Ghostbusters (1984).

During a varied career, he was Frank Sinatra's publicist and Steven Spielberg's agent and confidant, making the deals that secured artistic freedom and a fortune for the young director before his 30th birthday. He was a partner in the early days of International Creative Management (ICM), one of the biggest showbiz talent agencies in the world.

In her infamous memoir You'll Never Eat Lunch in this Town Again (1991), Julia Phillips, who produced Spielberg's Close Encounters of the Third Kind (1977), described McElwaine as “the most immaculate man in Hollywood”. “He represents a substantial portion of the promising young film-makers of the time. I assume that means he is a very good agent.” However, there was “too much gold” and “too many wives” for her taste. “He admits to five, but we know there are more.”

Guy McElwaine was born in Hollywood in 1936. His father was a publicist for MGM. He attended the University of Southern California on a baseball scholarship but reputedly lost it after a row over him playing minor league professional baseball.

After working in the Paramount mail room, he followed in his father's footsteps, joining the publicity department at MGM. He had a spell with the PR company Rogers & Cowan and then launched his own PR and management company, representing Sinatra, Warren Beatty, Judy Garland, the Righteous Brothers, and the Mamas and the Papas.

In 1969 he joined Creative Management Associates (CMA, predecessor of ICM), and linked up with the young Spielberg, who was trying to break out of TV and into movies. Spielberg was not only McElwaine's client, he also became part of his social circle, which also included the producer Alan Ladd.

In 1973 when Spielberg was awaiting the release of The Sugarland Express, his first made-for-cinema feature film, he said: “When you make your first feature in this town, you're incredibly hot, and if you have a good agent, he'll make your next three deals - before your film comes out.

“I have a terrific agent and he has created the greatest hype ... At four studios he's got me carte blanche to do whatever I want for a reasonable sum of money.” His next film was Jaws (1975). It went way over budget and cynics predicted an early demise, but it became one of the biggest hits of all time. However, McElwaine threatened to end the relationship if Spielberg pursued his intentions of filming Flushed with Pride, a comic biopic about Thomas Crapper, the British inventor of the modern toilet. McElwaine felt it was a wrong turn and Spielberg abandoned the idea.

In the mid-1970s McElwaine accepted a position as senior executive vice-president, production at Warner Bros and worked on Dog Day Afternoon (1975) and All the President's Men (1976). But he soon returned to agency work at ICM, putting together whole “packages” of talent for films such as Close Encounters and ET (1982).

In the early 1980s McElwaine became president of Rastar Films, the company founded by producer Ray Stark and acquired by Columbia, and then president and subsequently chairman and chief executive of Columbia itself. He quit in 1986, amid rumours that he was about to be fired, and returned to ICM and a roster of clients that included Sharon Stone and Kim Basinger. He left to set up his own production company McElwaine/Hayes. It never really got going, but it did secure a deal with the powerful Morgan Creek film company, whose earlier hits included Robin Hood: Prince of Thieves (1991).

In 2002 McElwaine became president of Morgan Creek, a post he held till his death. During his time at Morgan Creek he was executive producer on several films including the Matt Damon thriller The Good Shepherd (2006).

He is survived by four children.

Guy McElwaine, Hollywood executive, was born on June 29, 1936. He died of pancreatic cancer on April 2, 2008, aged 71