Mark Allen has tendered his resignation as Rangers' director of football after just over two years with the Scottish Premiership club.
Rangers say it is "a blow" and he had decided to "move on for family reasons and in order to explore other options".
The former head of Manchester City's academy was responsible for taking Steven Gerrard to Ibrox as manager.
Gerrard said: "Mark's success here is evident for all to see and we would all like to wish him well moving forward."
Allen oversaw a busy summer of transfer activity at Ibrox, with nine permanent signings and six exiting the first-team squad.
It culminated in the £7m return of former loanee Ryan Kent from Liverpool on transfer deadline day, with Gerrard insisting it had not been a panic buy immediately after their 2-0 derby defeat at home to title holders Celtic and had been financed by qualification for the Europa League group stage.
"I would like to place on record my sincere gratitude to Mark for the incredible support he has shown to me and all of my staff since I came to the club 16 months ago," Gerrard told Rangers' website.
The Ibrox club say Allen "has helped move Rangers into a significantly stronger and more challenging position" after being "instrumental in successfully revamping the football department".
"Mark has made a hugely positive impact in bringing in a higher quality of first-team player and he has led the renovation and improvement of the Hummel Training Centre, making it fit for a club the size of Rangers," they stated.
Allen said it was "a privilege to work for Rangers, one of the biggest clubs in football" and that "I've loved every minute".
"Bringing Steven Gerrard to the club will always be a special point in my career and I would like to thank him, his excellent staff, the players and all the staff at Rangers for their support throughout my tenure," he said.
Managing director Stewart Robertson expressed his disappointment at Allen's decision.
"But we appreciate the impact he made during his time in Scotland and he leaves Rangers in a better place than when he first arrived," he added.
"Losing a man of his calibre is a blow, but the practices he put in place at the club will stand us in good stead for the future."