The Spider was a mysterious vigilante adventurer in the 1930s and 1940s whose exploits were initially chronicled in pulp novels. He was really millionaire Richard Wentworth.
In Tarzan Alive, Philip José Farmer revealed that Wentworth's parents were John Byron Wentworth (i.e. Lord John Roxton) and Rhoda Delagardie.
He also theorised that Wentworth had served as G-8 in the First World War, and that he had a split personality and accordingly was Kent Allard / The Shadow as well. Farmer retracted these ideas in Doc Savage: His Apocalyptic Life.
Dave McTaggart has suggested that Wentworth and his girlfriend Nita Van Sloan were the parents of Mack Bolan.