The star, who was the longest-serving cast member in the soap's history, had been off sick from the show for three months.
He was initially offered a three-month contract to play Jack Sugden and made his first appearance on screen on February 19, 1980.
An astonishing 28 years later - after Jack's three marriages and five children - he remained one of the show's most popular stars.
SEND YOUR TRIBUTES ON CLIVE HORNBY TO US. WE WILL PUBLISH THEM ALL.Series producer Anita Turner said: "This is a devastating loss and we are all deeply saddened. Clive will be greatly missed by everyone who has worked with him on
Emmerdale during the past 28 years.
"He was a hugely popular and well-respected member of the cast and a terrific actor. Our thoughts are with his family at this difficult time."
Clive was born in Liverpool and started out as an accounts clerk, before enjoying success as a drummer with pop group The Dennisons in the 1960s.
The band were compared to and played on the same bill as The Beatles at Liverpool's famous Cavern Club.
Later, the group split to pursue other projects and Clive turned his attention to acting, attending the London Academy of Music and Dramatic Art before going into repertory theatre.
Click here for Jack Sugden slideshowHe later appeared in TV shows including
Get Some In, Gerry Anderson's
Space 1999 and
Minder, alongside George Cole, before making his first appearance in
Emmerdale on February 19, 1980.
He was initially offered a three month contract as Jack Sugden, a character who returned to the village after previously being played by Andrew Burt.
Some of Jack's highlights include fighting to save his livestock during the
Emmerdale killer thunderstorm in 2003; while in 2004, he survived after being shot by his own son, village bad boy Andy Sugden (Kelvin Fletcher).
He was also involved in a massive storyline to mark the show's 35th anniversary last year, which saw him fighting for his life after his cottage exploded in a giant fireball caused by his teenage daughter Victoria (Isabel Hodgins).
Hornby, who died after suffering from an illness, requested that details relating to his health were not published.
Jack was the son of Jacob and Annie Sugden, whose family owned Emmerdale Farm since early in the show.
suzanne.mctaggart@ypn.co.ukJack Sugden timeline
1982 – Jack marries childhood sweetheart Pat Merrick, mother of his son Jackie
1984 – Jack has an affair with a market manager, but Pat forgives him
1986 – Their second son, Robert, is born. Later that year, Pat died in a car crash, leaving Jack a single dad.
1987 – Jack spends two weeks in jail for his part in an anti-nuclear dump protest
1989 – Jack's eldest son Jackie died in a shooting accident
1993 – Jack's stepdad Leonard is killed in the village plane crash. His mum Annie spends months in a coma.
1994 – Jack marries librarian Sarah Connolly after the birth of their daughter, Victoria
1995 – Robert runs away from home for four weeks. Later that year, Jack's brother Joe died in a car crash.
1997 – Jack had an affair with his step-niece Rachel.
2000 – Sarah dies in a barn fire. Jack is charged with murder – but found not guilty.
2004 - Jack is accidentally shot by Andy. Later that year, he marries Diane, who is suffering from colon cancer.
2007 - Jack is injured when his house explodes in a giant fireball caused by his teenage daughter Victoria, who blamed Jack for her mother's death.
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