Source: (pre-Crisis) Superboy vol.1 #183 (1972) / (post-Crisis) Superboy vol.3 #61 (1999)
Type: Imaginary story / Alternate EarthSuperboy #183 features an unmotivated imaginary story that asks What if Superboy's rocket had fallen in the jungles of Africa and he had been raised by apes? As he grows up, he gains more and more formidable powers, but still can't get no respect from fellow apes who call him "Hairless One". He avoids his landing site because of a kryptonite rock, but does go back to get his swaddling clothes from the crash and fashions them into a Superboy uniform. The "S" is simply the shape of the snake he defeated. Kirok--I mean, Karkan--goes on to fight poachers and animal thieves and embarks on a new life once he kisses the first human girl he's ever seen.
And Karkan is still part of continuity! Yes, thanks to the Hypertime story line in the modern day Superboy series, Karkan returned for a cameo.
He's out there! (Just don't tell Tarzan... he wants his shtick back.)