4. Jeff George
Jeff George only spent one season in Minnesota, back in 1999, but it was a memorable one. He ended up having one of the best seasons of his career that year, but it began as the backup to Randall Cunningham. Through six games that year, Cunningham did not fare well and wound up being benched.
George took over, led the Vikings to an 8-2 record under his direction while throwing for 2,816 yards, 23 touchdowns and 12 interceptions. He would actually lead the NFL in yards per completion at 14.7. George and the Vikings actually won a playoff game that year against the Dallas Cowboys, but would ultimately lose to the Rams, who went on to win the whole thing that season.
3. Teddy Bridgewater
Yes, this one counts. As a rookie back in 2014, Teddy Bridgewater began the season as a backup to veteran quarterback Matt Cassel. However, Bridgewater was thrust into action a few games into the season after Cassel went down with an injury. He ended up going 6-6 as a starter that year, throwing for 2,919 yards, 14 touchdowns and 12 interceptions.
The following season, Bridgewater was named the starter and went 11-5, throwing for 3,231 yards, 14 touchdowns and nine interceptions.
Of course, what ensued after that season was total tragedy. Bridgewater sustained a scary injury that might have put him out of the game forever, but he was able to come back and is still in the league today as one of the best backup quarterbacks out there.