The 71-year-old Scot announced on Wednesday morning that he will stand down at the end of the season after a trophy-laden 26-year reign, having celebrated his 49th and final piece of silverware with a 13th Premier League title this term.
Gill said: "I've had the tremendous pleasure of working very closely with Alex for 16 unforgettable years - through the treble, the double, countless trophy wins and numerous signings.
"We knew that his retirement would come one day and we both have been planning for it by ensuring the quality of the squad and club structures are in first-class condition.
"Alex's vision, energy and ability have built teams - both on and off the pitch - that his successor can count on as among the best and most loyal in world sport.
"The way he cares for this club, his staff and for the football family in general is something that I admire. It is a side to him that is often hidden from public view but it is something that I have been privileged to witness in the last 16 years.
"What he has done for this club and for the game in general will never be forgotten. It has been the greatest experience of my working life being alongside Alex and a great honour to be able to call him a friend."
Joel Glazer, joint chairman of the Manchester United board with brother Avie, pinpointed the 2008 Champions League final penalty shootout success over Chelsea as a highlight among the many memories.
He said: "Alex has proven time and time again what a fantastic manager he is but he's also a wonderful person.
"His determination to succeed and dedication to the club have been truly remarkable. I will always cherish the wonderful memories he has given us, like that magical night in Moscow."
Ferguson will take on the roles of both director and ambassador for the club after stepping aside from the managerial hotseat.
Avie Glazer said: "I am delighted to announce that Alex has agreed to stay with the club as a director.
"His contributions to Manchester United over the last 26 years have been extraordinary and, like all United fans, I want him to be a part of its future."