After playing college football for Northwestern in the late 1950s, he was signed as an undrafted free agent by the Pittsburgh Steelers. When during training camp he was switched to their defense, his attitude over the switch prompted him to play his position with too much aggression, and the coach of the 49ers asked him to quit "hammering" his players. Thus, "The Hammer" quickly stuck and became his nickname.
Williamson played one year for the Steelers in the National Football League in 1960. Next, he moved to the new American Football League. Williamson played four seasons for the AFL's Oakland Raiders, making the AFL All-Star team in 1961, 1962, and 1963. He also played three seasons for the AFL's Kansas City Chiefs.
During his period of playing for the Chiefs, Williamson became one of football's first self-promoters, nurturing the nickname "The Hammer" because he used his forearm to deliver karate-style blows to the heads of opposing players, especially wide receivers. Before Super Bowl I, Williamson gathered national headlines by boasting that he would knock the Green Bay Packers starting receivers, Carroll Dale and Boyd Dowler, out of the game. He stated "Two hammers to (Boyd) Dowler, one to (Carroll) Dale should be enough".
His prediction turned out to be an ironic one because "they (Green Bay) broke the hammer" as Williamson himself was knocked out of the game in the fourth quarter on the way to a 35–10 defeat. Williamson's head met the knee of the Packers' running back Donny Anderson. Williamson later suffered a broken arm from his own teammate when Chiefs linebacker Sherrill Headrick fell on him.
Williamson finished his eight-season pro football career in 1967 with a history of many hard tackles, passes knocked away, and 36 pass interceptions in 104 games. Williamson returned his interceptions for 479 yards and two touchdowns. After signing with the Montreal Alouettes of the Canadian Football League during the 1968 season, but not having played in a league game, Williamson retired.
Williamson became an actor much in the mold of star running back Jim Brown. He acted alongside Brown in films such as 1974's Three the Hard Way, 1975's Take a Hard Ride, 1982's One Down, Two to Go, 1996's Original Gangstas and 2002's On the Edge. He also guest starred with Brown in various television roles. In October 1973, Williamson posed nude for Playgirl magazine, preempting Brown's appearance in 1974. Williamson's early television roles included a role in the 1969 Star Trek episode "The Cloud Minders", in which he played "Anka". He also played Diahann Carroll's love interest in the sitcom Julia. In an interview for the DVD of Bronx Warriors, Williamson stated that his role in Julia was created for him when he convinced the producers that the Black community was upset that Julia had a different boyfriend every week.
Williamson's early film work included roles in M*A*S*H and Tell Me That You Love Me, Junie Moon. In 1973 he played the role of an African-American mafioso in the film Black Caesar and its subsequent sequel, Hell Up in Harlem. He also starred in the 1975 western film Boss Nigger, in which he played the title role. After this he appeared as an actor in several films, most of which are considered to be of the "blaxploitation" genre. In 1974, he starred alongside Peter Boyle and Eli Wallach in the movie Crazy Joe.
In 1974, he was selected by the ABC television network as a commentator on Monday Night Football to replace Don Meredith, who had left to pursue an acting and broadcasting career at rival network NBC. Williamson was used on a few pre-season broadcasts, but was quickly declared unsuitable by ABC. He was relieved of his duties at the beginning of the regular season, becoming the first MNF personality not to endure for an entire season. He was replaced by the fellow former player (and fellow Gary, Indiana, native) Alex Karras.
Since that time, Williamson has continued his career as an actor and director, recently appearing in the 2004 feature film version of the 1970s television series Starsky and Hutch.
In 1985, he co-starred in the short-lived series Half Nelson.
During the mid-to-late 1980s and early 1990s, Williamson frequently appeared on television as a spokesman for King Cobra ("Don't let the smooth taste fool you."), as did fellow actor/martial artist Martin Kove. In 1994, Williamson, along with many other black actors from the 'Blaxploitation' movie era (namely Antonio Fargas, Pam Grier, Rudy Ray Moore, and Ron O'Neal) made a cameo appearance on Snoop Doggy Dogg's music video "Doggy Dogg World", where he appears as himself using his pro-football nickname "The Hammer".
Williamson co-starred with George Clooney and Quentin Tarantino in 1996's From Dusk till Dawn, directed by Robert Rodriguez. He was in the cast of 1978's original The Inglorious Bastards, which would later inspire Tarantino's 2009 film of similar name.
Since the 1970s, Williamson has also been an active director and producer. His first film as producer was Boss Nigger (1975), in which he also starred. His second film as producer was in 1976 with Mean Johnny Barrows, a significant predecessor of the Rambo films which similarly featured a violent Vietnam Vet plot (though the novel First Blood on which the film First Blood was based was written in 1972). He has since directed over 20 features.
In the middle of the 1970s, Williamson relocated to Rome, Italy and formed his own company Po' Boy Productions, which started to produce actioners including Adios Amigo (1976) and Death Journey (1976), both of which starred and were directed by Williamson. Although his most recent efforts as director and producer have mainly been direct-to-video, Williamson has continued to remain active with films.
Fred Williamson has lately (from 2014–present) been prominent as a spokesman for the Wounded Warrior Project.
Fred Williamson in African American.