I think it’s fairly well known at this point that the greatest single season by a Chicago Bears’ quarterback (certainly in the modern era) was Erik Kramer in 1995. That season, Kramer completed 60.3% of his passes, for 3,838 yards, 29 touchdowns, and 10 picks. His 1.9% INT rate is the lower for any season in which a Bear QB threw for at least 2,500 yards, and the only Bear quarterback in that sample to best Kramer’s 7.21 ANY/A is someone named Rudy Buckich, who, in 1965, completed 56.4% of his passes for 2,641 yards, 20 touchdowns, and just 9 picks.