Paul Duffen admits the pressure resulting from Hull's poor results this season led him to resign as the club's chairman.
But he today wished the club continued success as they bid to retain their Barclays Premier League status.
Duffen stood down this morning after pressure mounted on him and manager Phil Brown following the club's poor start to their second season in the top flight, which has seen them take just eight points from their opening 10 games.
In addition, the club's accounts - finally released this week, five months behind schedule - showed borrowings of £22million, prompting accountants Deloitte to predict the Tigers will have to raise £23million to balance their books should they be relegated, and £16million if they survive.
Brown remains at the club and arrived at Hull's Cottingham training ground as usual to take this morning's session, but Duffen confirmed his departure shortly afterwards.
In a statement, Duffen said: "When I succeeded Adam Pearson as chairman of Hull City Football Club in June 2007 I was very aware of the responsibility to build on his legacy.
"I articulated an intention to take the Tigers to the previously uncharted waters of the Premier League and to the eternal credit of the players and coaching staff, that seemingly ridiculous ambition was achieved 11 months later thanks to a victorious debut appearance at Wembley in the play-off final.
"The start to our maiden top-flight campaign broke all previous records for a newly promoted side and ensured that 2008 will forever be remembered as the most remarkable year in Hull City's history.
"Football is a results business and in the same way that I enjoyed the successes of the previous two seasons, so I must take ultimate responsibility for the disappointments of 2009.
"It has been a tremendous privilege to lead the Tigers on this amazing journey and I pay tribute to all the staff for their hard work and dedication as well as to the fans for their magnificent support. I am proud to have played my part and wish the club every success in the future."
Pearson yesterday resigned as chairman of football at Coca-Cola Championship side Derby County, sparking suggestions he is set to return to East Yorkshire.
The Tigers will reveal more regarding the future control of the club at boardroom level early next week.
A statement - released via their official website, www.hullcityafc.net - confirmed: "The club has received a letter of resignation from Paul Duffen, executive chairman of Hull City AFC and Superstadium Management Company Ltd, which has been accepted and is effective immediately.
"The club wishes to express its gratitude to Paul for his outstanding contribution as chairman during a period of unprecedented success for Hull City AFC.
"The recruitment process has commenced in respect of the appointment of a new executive chairman and a further statement in relation to this will be issued by the club on Monday 2nd November."