In 2012, Peyton Manning was released by the Indianapolis Colts after he missed that entire season due to a neck injury. He then signed with the Denver Broncos. There were a number of factors that likely influenced his decision to sign with Denver.
First, Manning was familiar with the Broncos organization. He had played against them numerous times throughout his career, and knew some of the players and coaches on the team. Second, Denver is a city with a relatively mild climate, which would be beneficial for someone coming off of an injury. Third, the Broncos had just hired John Elway as their Vice President of Football Operations, and he was someone that Manning respected and trusted. Finally, the Broncos also had one of the best defenses in the league at that time, which would help offset any rust that Manning may have had from missing an entire season.