Alfonso Williamson (March 21, 1931 – June 12, 2010) was an American cartoonist, comic book artist and illustrator specializing in adventure, Western, science fiction and fantasy.

Born in New York City, he spent much of his early childhood in Bogotá, Colombia before moving back to the United States at the age of 12. In his youth, Williamson developed an interest in comic strips, particularly Alex Raymond's Flash Gordon. He took art classes at Burne Hogarth's Cartoonists and Illustrators School, there befriending future cartoonists Wally Wood and Roy Krenkel, who introduced him to the work of illustrators who had influenced adventure strips. Before long, he was working professionally in the comics industry. His most notable works include his science-fiction/heroic-fantasy art for EC Comics in the 1950s, on titles including Weird Science and Weird Fantasy.

In the 1960s, he gained recognition for continuing Raymond's illustrative tradition with his work on the Flash Gordon comic-book series, and was a seminal contributor to the Warren Publishing's black-and-white horror comics magazines Creepy and Eerie. Williamson spent most of the 1970s working on his own credited strip, another Raymond creation, Secret Agent X-9. The following decade, he became known for his work adapting Star Wars films to comic books and newspaper strips. From the mid-1980s to 2003, he was primarily active as an inker, mainly on Marvel Comics superhero titles starring such characters as Daredevil, Spider-Man, and Spider-Girl.

Williamson is known for his collaborations with a group of artists including Frank Frazetta, Roy Krenkel, Angelo Torres, and George Woodbridge, which was affectionately known as the "Fleagle Gang". Williamson has been cited as a stylistic influence on a number of younger artists, and encouraged many, helping such newcomers as Bernie Wrightson and Michael Kaluta enter the profession. He has won several industry awards, and six career-retrospective books about him have been published since 1998. Living in Pennsylvania with his wife Corina, Williamson retired in his seventies.

Williamson was inducted into the Will Eisner Comic Book Hall of Fame in 2000.

Al Williamson was born in Manhattan, New York City, New York, one of two children of Sally and Alfonso Williamson, who was of Scottish descent and a Colombian citizen. The family relocated to Bogotá, Colombia, when Al was two years old. "My father was Colombian and my mother was American," Williamson said in 1997. "They met in the States, got married and went down there. I grew up down there so I learned both English and Spanish at the same time. It was comic books that taught me to read both languages." At age nine, Williamson took an interest in comic strips via the Mexican magazine Paquin, which featured American strips as well as Underwater Empire by Argentine cartoonist Carlos Clemen. Later, Williamson was attracted to Alex Raymond's Flash Gordon strip after his mother took him to see the Flash Gordon Conquers the Universe movie serial. While living in Bogotá he met future cartoonist Adolfo Buylla, who befriended him and gave him artistic advice. At age 12, in 1943, Williamson moved with his mother to San Francisco, California; they later moved to New York.

In the mid-1940s Williamson continued to pursue his interest in cartooning and began to take art classes with Tarzan cartoonist Burne Hogarth, and later at Hogarth's Cartoonists and Illustrators School. There he met future cartoonists Wally Wood and Roy Krenkel. According to Williamson, "Roy broadened my collecting horizons, he became my guide to all the great illustrators — the artists who directly influenced adventure cartoonists like [Alex] Raymond and [Hal] Foster. He showed me J.C. Coll, Franklin Booth, Joseph Franke, Dan Smith, Norman Lindsay, Fortunino Matania, and the great Blue Book illustrators like Herbert Morton Stoops and Frank Hoban." As he continued to learn about the cartooning field, he would visit the comic-book publisher Fiction House, meeting such artists as George Evans, Bob Lubbers, John Celardo, and Mort Meskin.

Williamson's first professional work may have been helping Hogarth pencil some Tarzan Sunday pages in 1948, although Williamson, who had initially believed so, reconsidered in a 1983 interview and recalled that his Tarzan work had come after his first two pieces of comic-book art: providing spot illustrations for the story "The World's Ugliest Horse" in Eastern Color's seminal series Famous Funnies #166 (May 1948), and a two-page Boy Scouts story, his first comics narrative, in New Heroic Comics #51 (Nov. 1948). (Williamson is also identified as co-penciler, with Frank Frazetta, of a three-page crime story, "The Last Three Dimes", in Standard Comics' Wonder Comics #20 [Oct. 1948].) Williamson explained that while Hogarth had offered him Tarzan work, Williamson "just couldn't do it. ... I couldn't get it into my little brain that he wanted me to do it exactly the way that he did it," and instead successfully recommended Celardo, artist of the Tarzan-like feature "Ka'a'nga" in Fiction House's Jungle Comics. As Williamson recalled: