Selected in the first round of the 1965 NFL Draft out of Duke, Mike "Mad Dog" Curtis arrived in Baltimore with a reputation for raw, unchecked intensity. Initially deployed as a fullback on offense during his rookie season, the Colts quickly realized his vicious hitting and fiery demeanor belonged on defense. Upon shifting to linebacker in 1966, Curtis became the terrifying, central enforcer of a Baltimore defense that routinely punished opposing backfields.

Curtis weaponized a reckless, sideline-to-sideline playing style that made him one of the most feared middle linebackers of his generation. Known for his zero-tolerance attitude on the field—famously leveling a fan who ran onto the field to steal the game ball—Curtis proved to be as skilled as he was intimidating. His career reached its zenith in 1970, when the Kansas City Committee of 101 named him AFC Defensive Player of the Year. That same season, Curtis provided the defining play of Super Bowl V against Dallas: with the game tied late in the fourth quarter, he intercepted a Craig Morton pass and returned it to the Cowboys' 28-yard line, setting up Jim O'Brien's game-winning field goal to secure Baltimore's 16–13 victory.

A four-time Pro Bowler (1968, 1970, 1971, 1974) and a First-Team AP All-Pro selection in 1968, Curtis anchored the Colts' defense through both their 1968 NFL Championship and Super Bowl V title runs. Although sacks weren't officially recorded in the NFL then, PFR retrospective research credits him with 16.5 sacks during his Baltimore tenure, complementing his elite pass coverage. Curtis spent 11 seasons terrorizing offenses in blue and white before finishing his career with brief stops in Seattle and Washington.

For the Colts, Curtis accumulated 21 interceptions for 248 return yards, two defensive touchdowns, eight fumble recoveries, 16.5 unofficial sacks, and when you count his numbers elsewhere, he is an unofficial member of the defensive 20/20 club.