Tak is the main antagonist of Invader Zim episode "Tak: The Hideous New Girl". She is female Irken warrior. Her main goal is to take Zim's "mission" because Zim had ruined her training as an Invader. Vicious and determined, she is more focused on trying to gain for herself an honorable title as an Invader than revenge; Zim just happens to be in the way of getting it.
Fifty Earth years prior to Zim's arrival on Earth, Tak was going through training to become an Irken Elite, with the possibility of being chosen as an Invader. Zim, however, caused a major blackout throughout half of Devastis when he chose to retrieve a snack from a faulty vending machine by using a large robot to shoot straight at it.
The resulting explosion blasted half the planet's power grid and trapped Tak in a training cell on the day of examination. Despite the catastrophic power outage, all tests continued on the other still-working side of the planet, leaving Tak stranded. She pled her case to her assigned Control Brain in hopes for some leniency, but her request was promptly denied. She was put into a janitorial squad to do hard labor on Planet Dirt for the duration of seventy Earth years before she could retake the examination.
Her ship however crashed in Dib's yard. Discovering that Zim was on the planet, Tak resolved to prove herself and get revenge on Zim by taking over Earth.
Despite the fact that she appears in only one episode, it is clear that Tak's defining characteristics are that she's vindictive, cruel, mysterious and rather cunning. Despite this, Tak does seem to have a more sophisticated side. She's shown to have a far more advanced disguise than the actual invaders, choosing a hologram over a paper-thin disguise, and taking advantage of the population's obliviousness. Because she is only featured in a single episode, her personality is not explored to an extensive degree. However, it is very clear that she is a more-than-capable Invader. Oftentimes her behavior is misread by audiences as denial of wanting revenge. However, the suffering she inflicts on Zim before revealing herself can be interpreted as not just a joy but a means to throwing him off-track while she constructed an enormous magma pump disguised as a Deelishus Weenie stand. She states that she doesn't want revenge, but to claim what's rightfully hers.