Alan Simpson of writing duo Galton and Simpson has died at the age of 87, his manager has said.
The pair created sitcoms including Hancock's Half Hour and Steptoe and Son.
Simpson had undergone a "long battle with lung disease", manager Tessa Le Bars said.
Ray Galton's family said there were "no words" to express their feelings at the death of "Ray's partner and family friend over the last 70 years".
'A lifetime of work'
Simpson and Galton met at Milford Sanatorium in Surrey as teenagers, having both been diagnosed with tuberculosis, and started writing for the hospital's radio station.
They went on to write television, film and stage scripts for stars including Peter Sellers, Leonard Rossiter and Frankie Howerd.
The pair were honoured with a Bafta fellowship last year and had been made OBEs in 2000.
Bafta said it was "deeply saddened" at the news of Simpson's death.
A statement from Ray Galton and his family said: "From their first attempts at humour in Milford sanatorium, through a lifetime of work together, the strength of Alan and Ray's personal and professional bond was always at the heart of their success."
Le Bars said: "Having had the privilege of working with Alan and Ray for over 50 years, the last 40 as agent, business manager and friend, and latterly as Alan's companion and carer, I am deeply saddened to lose Alan after a brave battle with lung disease."
Galton and Simpson are credited with bringing social realism to British comedy.
Hancock's Half Hour started as a radio show in 1954, before transferring to television. It was aired on the BBC from 1956 to 1960.
Their biggest TV hit however was Steptoe and Son, about father-and-son rag and bone team Harold and Albert, and their lives in a squalid home.
It ran for 12 years, from 1962 to 1974, reaching an audience of 28 million.
Both series were revived last year as part of the BBC's Lost Sitcoms series.
Tributes have been paid to Simpson, with comedian Paul Merton saying: "Long before I met him, Alan Simpson was a comedy hero of mine. In the flesh he didn't disappoint.
"In the 20 odd years that I knew him Alan was always, wise, funny, loyal and opinionated. He loved good food, good wine and Hampton and Richmond football club. In fact, all the finer things in life."
He noted that Galton and Simpson's Steptoe and Son had "brought a new realism into situation comedy, which is still very much part of the genre today".
Comedian and author David Walliams tweeted: "Alan Simpson was half of one of the greatest comedy writing duos of all time with Ray Galton 'Hancock' & 'Steptoe & Son' are masterpieces."
Writer Neil Gaiman tweeted: "I was lucky enough to meet & interview him & Ray Galton in 1985.
"They changed radio comedy, then TV comedy."
Broadcaster Danny Baker called Simpson "an absolute giant". He tweeted: "No praise too high for what he & Ray created. Honoured to have shaken his hand."