Brian Urlacher ranks the greatest MLB in Bears' history

The middle or inside linebacker (MLB), sometimes called "Mike," is often referred to as the "quarterback of the defense". Often it is the middle linebacker who receives the defensive play calls from the sideline and relays that play to the rest of the team–and in the NFL he is usually the defensive player with the electronic sideline communicator. A jack-of-all-trades, the middle linebacker can be asked to blitz (though they often blitz less than the outside linebacker), cover, spy the quarterback, or even have a deep middle-of-the-field responsibility in the Tampa 2 defense. In standard defenses, middle linebackers commonly lead the team in tackles. The terms middle and inside linebacker are often used interchangeably;[2] they are also used to distinguish between a single middle linebacker playing in a 4–3 defense, and two inside linebackers playing in a 3-4 defense.

The Bears have fielded four of the best middle linebackers in NFL history: Dick Butkus, Bill George, Mike Singletary and Brian Urlacher. Today, all four men are enshrined in the Pro Football Hall of Fame.

Well, here is a video where Urlacher answered the question as to which one was the best MLB in Bears' history.