1. Gary Kubiak, 1983-1991
You've got to have Gary Kubiak on top of your list as the best backup QB in Denver Broncos history, right? He made his entire NFL career out of being John Elway's backup.
Kubiak came into the NFL the same year as John Elway, 1983. He was an 8th-round pick out of Texas A&M who appeared in 119 career NFL games but didn't even throw 300 total passes. That doesn't matter. He had one of the most important jobs in pro football at the time, backing up superstar QB John Elway.
And Kubiak did it well.
He helped the Broncos to a 3-2 record when he was called upon, and he orchestrated three game-winning drives during his NFL career. Kubiak even added a couple of rushing touchdowns, too.
He wasn't being coveted by anyone as a possible starter, but that didn't matter. His contributions went further than simply the impact he was making on the field. Kubiak saw the game exceptionally well, which is why he quickly transitioned from playing into coaching in the 1990s. Kubiak was the running backs coach at Texas A&M for a couple of seasons before joining Mike Shanahan's staff in San Francisco as the team's QBs coach.
He followed Shanahan to Denver in 1995 when Shanahan was given the reins of the Denver Broncos and got his first offensive coordinator gig. Kubiak would hold that role for a long time, almost the entirety of Mike Shanahan's tenure with the team. From 1995-2005, Kubiak was the Broncos' offensive coordinator.
He then became the head coach of the Houston Texans in 2006 and did a very good job from 2006-2013 before he was let go. He helped the Texans win multiple AFC South division titles and made that franchise relevant.
John Elway hired Kubiak as the Denver Broncos head coach during the 2015 season and it's fair to say that Kubiak was one of the primary missing ingredients for the team. He coached them to a win in Super Bowl 50 in his first year on the job and his coaching was a huge edge as the Broncos were borderline unbeatable in one-score games that season.