Middlesbrough chief executive Keith Lamb is standing down from his position after almost 25 years with immediate effect.
Lamb worked alongside chairman Steve Gibson as the Teessiders fought back from the brink of financial disaster to enjoy the most successful spell in the club's history, during which they won the Carling Cup in 2004 and reached the UEFA Cup final two seasons later.
He will remain on the board as a non-executive director as Gibson and new manager Tony Mowbray attempt to steer Boro back into the top flight.
Lamb said: "After almost 25 years in the role during some of the most challenging, exciting and successful periods in the club's history, the time is right for me to make way for someone else.
"I have enjoyed every minute of my time as chief executive and now look forward to exploring new opportunities and challenges.
"I want to thank all the staff who have given me their help and support during my time at the club. I am pleased that with Tony Mowbray and [assistant manager] Mark Venus at the helm, the club is able to look forward to an exciting future.''
Lamb has played a central role in the club's wheeling and dealing in recent years, working closely with successive managers on transfers and contracts.
Gibson, who saved Boro as they almost went out of existence in 1986, paid tribute to his contribution.
He said: "I want to thank Keith for his integrity, commitment, dedication and loyalty to the club and to me personally.
"Keith's involvement has been crucial to the most successful period in the club's history, including not only the move to the Riverside Stadium and the development of the Rockliffe training facility, but also winning our first major trophy and reaching a European final.
"I am delighted that Keith will continue to work with the club as a non-executive director, and this will enable us to draw on his wealth of experience and talent to fashion the future strategy of the club.''