Doofengung lives alone in a decaying cave, where he amuses himself by watching stalactites dripping. Every once in a while, he grows jealous of his more highly-evolved brother Ro-juh, and comes up with schemes to steal Ro-juh's home. He is generally thwarted by Bunka da Bunkaquan, though it turns out that Bunka has nothing to do with foiling Doofengung's schemes at all.
Doofengung is physically very similar to his present-day self, with the exception that Doofengung has a quiff-like hairstyle, a more pronounced brow, and buckteeth.
Personality and traits
Doofengung is very simple-minded, and even more childish than the modern-day Doofenshmirtz. He is very easily amused, finding dripping stalactites especially funny. Doofengung is also very unhappy with his lot in life as a Neanderthal, and believes he deserves a more comfortable lifestyle than his cave.
Skills and abilities
Doofengung has the ability to build very simple tools, such as his Stick-inator and a cage made of bones. He is also capable of forming surprisingly complicated ideas, such as the principle of evolution. However, he is not very well coordinated, as it took him several tries to set up a ladder correctly. He's just as unable to recognize Bunka da Bunkaquan without his horned animal skull as Heinz Doofenshmirtz is unable to recognize Perry the Platypus without his fedora hat.
In the script of the episode he is named Gunka-lunk, which explains why the evil jingle goes "Gunka-lunk Gunka-lunk, Gunka-lunka." The same happens in the end credits of the episode.