Troll

Trolls are the dominant species of the planet Alternia. They are a hyper aggressive race of insect-like humanoids with some physiological distinctions based on the color of their blood.

Trolls are first seen in text on HS 859 (page 859) when Karkat trolls Jade, and are first seen visibly on HS 1353 (page 1353) when Spades Slick sees Karkat on the monitor in the command station underneath The Felt's mansion.

Typing Quirks
A particularly notable aspect of troll culture is typing quirks. Every troll has a unique way of typing that reflects some aspect of their personality. While humans also have a particular way of typing, trolls particularly type in ways that humans find unorthodox.

Temporal Mechanics
According to Kanaya Maryam in HS 1093 (this early conversation), trolls are easily capable of grasping time mechanics from as young as infancy. How much of this claim is true and how much is exaggeration is not made explicitly clear.

Miscellaneous
The names of troll movies are extremely long, literal, and descriptive of the plot. Karkat claims this is because Alternia has HS 1603 (racked up thousands of years of film history). Due to their length, these names aren't usually used for casual conversation.