Steven Gerrard has been appointed Rangers manager on a four-year deal.
Gerrard, 37, has been working as a Liverpool academy coach since April last year, but will take up his new position at Ibrox at the end of the season.
"I am honoured to become the next manager of Rangers," said Gerrard. "I have enormous respect for this football club, and its history and tradition.
"I can't wait to start this new journey at Rangers as we look to build on the many successes that this club has achieved."
Allen said: "From the moment we met with Steven to discuss this opportunity, we felt that his ambitions and desire to succeed equalled our own for the club.
"Make no mistake, Steven fully understands the demands that come with managing a club of this stature and we look forward to exciting times ahead."
Rangers chairman Dave King added: "From the very beginning, talks have been extremely positive and we believe that Steven is the right man to drive Rangers forward.
"He was extremely impressive throughout our negotiations and we are convinced that he has the necessary knowledge and temperament to lead the club to the success we all desire."
Rangers said details about Gerrard's backroom team would be revealed at a later date, but Sky sources understand former Liverpool team-mate Gary McAllister will be his assistant.