3. Tony Romo (2003-2016)
Regular season record: 78-49
No. 1 All-Time Cowboys Passing Yardage: 34,183
There's this very unfair narrative around Tony Romo that he's an underachiever. While it's true he never won a title, No. 9 should go down as one of the biggest overachievers in the history of the NFL.
Despite setting multiple passing records at Eastern Illinois, Romo was only asked to come to the 2003 Scouting Combine as an extra arm. They didn't want the good prospects to tire out throwing the ball, so they asked players such as Romo to show up.
Once there, he caught the eye of a couple of teams including the Cowboys and Denver Broncos. Of course, each team already had him on the radar since Sean Payton (who was the offensive coordinator in Dallas at the time) and Mike Shanahan (Denver's coach that year) were both Eastern Illinois products as well.
Romo still went undrafted and chose Dallas over Denver, which proved to be a great move for both parties. He spent three seasons on the bench before Bill Parcells finally gave him a shot in Week 7 of the 2006 campaign. Romo replaced an ineffective Drew Bledsoe and proceeded to break every passing record in team history.
By the time his career was done, Romo had the most passing yards in team history with 34,183 as well as the most touchdowns with 248. He also has the single-season record for yards with 4,903 in 2012 and is second in touchdowns with 36 in 2007.
As a regular-season quarterback, Romo was electric and went 78-49 as a starter and has nearly every important passing record for one of the most storied franchises in league history. That's despite being undrafted. However, his inability to get it done in the postseason is why he didn't crack the top two — and why he's unfairly called an underachiever.