West Ham joint-chairman David Gold has died aged 86 following a short illness, the club has confirmed.
The lifelong Hammers fan, who took charge in January 2010 alongside business partner David Sullivan, helped oversee the club's transition from a Premier League also-ran to a European contender.
Under Gold, the club earned sixth and-seventh-place finishes over the past two seasons, and reached the semi-finals of the Europa League last year.
In a statement, manager David Moyes paid tribute to Gold, who also played as a schoolboy for the club during his youth.
"I am extremely sad to hear this news," he said. "On behalf of all of the players and my staff at the training ground, I would like to extend our deepest sympathies to David Gold's family at this very difficult time.
"It was clear that he had a genuine and sincere love for the club and was a true supporter at heart. He will be greatly missed."
Sullivan also paid his respects, adding: "Of all our joint ventures, none gave us more pride and happiness than the day we took ownership of West Ham United.
"David had a long-standing connection with the Hammers, having grown up opposite the Boleyn Ground in Green Street.
"He always wanted what was best for West Ham United, and his passing is a great loss for all of us."
The club confirmed a further tribute would take place in due course, with the Hammers due to travel to fellow strugglers Leeds United on Wednesday.