Garbog was an alien who visited Earth to make a study about human mothers for entirely unexplained reasons.
Phineas and Ferb repaired Garbog's spaceship while Garbog was collecting information about the human female parental unit by disguising himself as Linda. Phineas states that Garbog is a friend of Meap ("Invasion of the Ferb Snatchers"). Similarly to Meap, Garbog speaks a totally untranslatable language when not being translated by alien technology (in this case, a robot of Linda Flynn).
Garbog doesn't seem to know much about humans, as it tried to shoo away a piece of poultry, calling it a "skin bird."
He is smaller than Meap, having the size of Linda Flynn's head. He is green and has tentacles down from his face. He also has the ability to fly or hover, though it is unknown if this ability is due to the effects of technology. He wears a dark blue shirt that has a very large collar on top, and for bottoms, he wears black capri pants with no shoes.