Tak is an Irken. She was going to be an Invader, but due to the power outage that Zim caused on the planet she was on, she was unable to become one.
She has the personality of a maniac, though is clever and quick on her feet when it comes to situations. She seems to be bent on getting revenge for what Zim did, even though she stated that "it isn't about revenge".
Her disguise is actually a perfected hologram, with the only flaw being that she still only has three fingers. Her S.I.R. unit, Mimi (shown below), is altered as well, and has a hologram disguise of a cat with horned ears.
Tak's ship was taken in by Dib after she was ejected in "Tak: The Hideous New Girl". It has her personality downloaded into its hardware, though can be replacable as shown in "Backseat Drivers From Beyond the Stars ".