The heaviest player to ever play in the NFL was former Lions offensive lineman Aaron Gibson, who was listed at four-hundred ten (410) pounds. Gibson played for the Detroit Lions, Dallas Cowboys, and Chicago Bears over his seven year NFL career. Gibson was listed as weighing over four-hundred forty (440) pounds in high school.
The only other players to crack the 400-lb mark are Nate Newton and Terrell Brown. Other notable heavy players include Michael Jasper, Trent Brown, and William "The Refrigerator" Perry. Perry, who was a defensive lineman, occasionally played fullback in goal-line situations and even scored a rushing touchdown in Super Bowl XX.
Weight is a key attribute for offensive and defensive linemen because they need to be able to physically overpower their opponent. Strength is key in blocking and rushing-it takes a lot of weight to stop a lot of weight.