4. Brett Favre
Pound-for-pound, Brett Lorenzo Favre had to be the toughest quarterback in NFL history. At 6-2, 222, Favre endured as much abuse as any quarterback to ever play the game, yet he still managed to start 321 consecutive games, regular and postseason combined, for three different franchises, the Packers, Jets and Vikings.
The majority of that time was with Green Bay, as he lead the Pack to their first Super Bowl title in the post-merger era, and first one that really counted (the first two Packer Super Bowl triumphs were basically glorified exhibition games).
Favre remains the only player to win three consecutive NFL MVP awards (1995-1997). When Favre retired, he held many NFL passing records that have since broken by Peyton Manning and/or Tom Brady.