The Alabama legend released a touching tribute on Tuesday ... saying, "Mike Leach was a friend, and we are deeply saddened by his unexpected passing."

"I thoroughly enjoyed getting to know Mike over the last several years. I never knew quite where our conversations were going, but they always made me smile."

Saban praised Leach as an offensive mastermind ... who was well-respected by his peers.

"His teams were well-coached and challenging to defend. They played with poise and toughness, which is a credit to his leadership."

Kingsbury -- who played under Leach at Texas Tech -- added, "There is no way I would be where I am today if not for Mike Leach and everything he taught me about the game. Truly one of the most innovative offensive minds in football, he was more than a coach."

"He was a mentor, a friend and one of the most special people l've ever met. My heart goes out to Sharon, the Leach family and everyone who who had the privilege of knowing and loving him."

"Our sport was better because of Mike Leach and is far less interesting without him."