1. Rod Smith (1994-2007), WR
Let's get the obvious one out of the way. Rod Smith played all 14 of his NFL seasons with the Broncos, was a two-time All-Pro, led the league in receptions in 2001, posted eight 1,000-yard seasons, and won a couple of Super Bowls in 1997 and 1998. The franchise's all-time receiving leader went undrafted out of Missouri Southern in 1994, but Smith quickly made a name for himself. His first NFL catch was a game-winning "Hail Mary" contested by Hall of Fame corner Darrell Green. From there, Smith rose on the depth chart and became the top wideout in Denver's offense until he retired following the 2007 season.
Smith recorded at least 70 receptions in every season from 1997 to 2005. During that stretch, Smith posted two seasons with 100 or more receptions and six straight seasons with at least 1,000 receiving yards. He is responsible for many great Broncos memories like his 80-yard touchdown in Super Bowl XXXIII, and his 1,602-yard season in 2000, but something that gets lost in the conversation is his blocking prowess. He spent the entirety of his career clearing paths for the likes of Terrell Davis, Clinton Portis, and every other Shanahan back in a run-heavy offense. He famously did not record a catch in Super Bowl XXXII, and he famously did not care. He was the exact opposite of your typical diva star receiver, and he played with a chip on his shoulder that led him to the Broncos Ring of Fame.
Rod Smith finished his career with 11,389 receiving yards, over 2,000 yards more than the second all-time leading Broncos receiver, Demaryius Thomas. He was a legendary pass-catcher and one of the best blockers the position has ever seen. Smith is by far the greatest undrafted Bronco of all time, and he has a strong case to be named the greatest undrafted wideout in league history.