A graduate of Jackson State University, he was a teammate of Walter Payton. Drafted in the third round of the 1976 NFL Draft, Slater seldom played his first few years before starting in 1979. Known as the most consistent member of one of the most potent offensive lines in NFL history, Slater was selected to seven Pro Bowls and broke a record for most seasons with one team. His jersey number was retired and he was inducted to the Pro Football Hall of Fame in 2001.
Although used primarily as a backup and special teams player during his first three seasons, Slater became the starting right tackle in 1979. That year the Rams went to Super Bowl XIV, where he successfully defended L.C. Greenwood from getting a quarterback sack. In 1980, he was a part of an offensive line that surrendered just 29 sacks and helped the Rams’ offense finish second in the NFL in total yards gained with 6,006. In 1983, he and the Rams offensive line demonstrated their versatility when they allowed a league-low 23 sacks while also paving the way for Eric Dickerson’s rookie rushing record of 1,808 yards. In 1985, he was the key blocker for Dickerson as he ran for a playoff record 248 yards and two touchdowns against the Dallas Cowboys in a NFL divisional game. During the 1987 NFL strike, Slater was one of the few veterans who crossed the picket line. During a 1989 playoff game, Slater prevented Reggie White, who was considered the premium pass rusher in the NFL, from sacking the quarterback, a game that Slater later became best known for. Slater was considered by critics the most consistent lineman on one of the best offensive lines in the NFL, which also included Pro BowlersKent Hill and Dennis Harrah and was regonized for his "work ethic and leadership skills" when he was inducted to the Hall of Fame. He retired after the 1995 season when injuries reduced him to playing one game the entire year. He is the only player in league history to play for one single team/franchise in three different cities (Los Angeles 1976-1979, Anaheim 1980-1994, and St. Louis 1995)
His son Matthew, who played college football at UCLA, was drafted by the New England Patriots in the fifth round of the 2008 NFL Draft. He is currently a gunner, and special teams captain for the Patriots. The Slaters have 12 Pro Bowl nods between them, and his son's nominations to the Pro Bowl makes the Slater family the third most nominated family in the NFL (only the Manning family (Archie, Peyton and Eli) and the Matthews family (Bruce, Clay Jr and Clay III)] have more Pro-Bowl nominations as a family). Slater is active with the NFL Play 60 program, which sends NFL players to schools to discuss spending 60 minutes a day to participate in sports activities. Another son, David is in his final year in college, and Slater and his family live in Los Angeles.