Alexander Crichlow Barker Jr. was a direct descendant of the founder of Rhode Island, Roger Williams, and of Sir William Henry Crichlow, historical Governor-General of Barbados. Barker attended the Fessenden School and Phillips-Exeter Academy, where he excelled in football and track. He went to Princeton, but left to become an actor. A year later he was spotted while working in summer stock theatre, and received a contract offer from 20th Century Fox. World War II intervened; he enlisted as an infantry private, and rose to the rank of major.

Although later signed by Fox and then Warner Bros, he was too tall for supporting parts and too unknown for leads. Tarzan's Magic Fountain (1949) (RKO) provided his first starring role. After five Tarzan films, he went into other adventure films. After 16 non-Tarzan films, mostly westerns, he went to Europe in 1957 (he spoke French, Spanish, Italian, and German). He went on to make more than 50 more films worldwide: Brazil, Germany, Spain, Yugoslavia, Italy, Lebanon, France, as well as the USA. He became very popular in Germany owing to his roles as "Old Shatterhand", "Kara Ben Nemsi", and "Dr. Karl Sternau", in films based on books written by Karl May, a popular German writer of adventure literature. Barker won Germany's Bambi Award as Best Foreign Actor of 1966.