The Utroms are a species of small, tentacled aliens, vaguely resembling brains who appear in the TMNT comic strips.
The Utroms, as a species, come to the attention of the Turtles during the events of Magic Turnstone. Though they already knew Krang, they did not know he was an Utrom until they noticed that Gumpa, the Turnstone hologram tutorial display, looked like Krang. When Donatello asks the Turnstone to search its files for references to "Krang", the answer is that Krang was banished from the Utrom Empire on 3874.7.024 for criminal activity.
Donatello then asks for the files for the Utrom Empire. Gumpa says that the Utrom Empire is a group of galactic species unified under common law and dedication to science. The Utroms greatest technological advances include the transmat teleporter, metamorphic mutagen chemical, and child-proof caps. Don then asks his brothers if they know what this means - that the same beings that created the Turnstone also created - mutagen.
Suddenly, another Utrom appears to inform the Turtles that they must see them and must bring them to their world now. The Turtles are then teleported to the Planet Utr.