Belkar Bitterleaf is one of the main characters in the Order Of The Stick. Though he is considered to be one of the protagonists in the comic, he is rather selfish and sadistic in nature.
Belkar Bitterleaf was recruited to the Order Of The Stick to serve as the party's tracker. However, it quickly became apparent to the rest of the Order Of The Stick that he did not actually enter the dungeon to kill Xykon for the good of others, and that he simply wanted to slay goblins so that he could take their treasure.
After the Dungeon Of Dorukan exploded, he accompanied Haley and Vaarsuvius to rescue Elan after he was captured by bandits...during which he almost got them killed when he chose to set a tent on fire despite Haley telling not to do, which attracted their attention. He also accidentally set a hotel on fire, which caused Haley's treasure to be destroyed.
Afterwards, he and the rest of the Order Of The Stick (with the exception of Durkon, who came with her voluntarily) were captured by Miko Miyazaki, he immediately developed a hatred towards her. As he escaped from solitary confinement, he killed the guard assigned to him.
Realizing how psychopathic Belkar was, Roy (the leader of the Order Of The Stick) had Lord Shojo place a Mark Of Justice on his head to prevent him from harming anyone else.
This would cause him to become seriously ill if he chose to murder someone within the bounds of a city, strayed too far from Roy, or angered him enough to activate the seal. He eventually activated it after he chose to murder the Oracle (who had foreseen his death at his hands, and set up a kobold village in order to mock him).
This magical mark was eventually deactivated by a priest of Loki, just after a vision of Lord Shojo taught him to fake character development during a dream sequence.
However, he has become less (overtly) evil as the comic has gone on. During the War Of XP, he killed an assassin that wanted to kill Lord Hinjo. He was awarded with a plethora of hobgoblins that he was allowed to kill as he had fallen outside of city limits. He also rescued Haley from Crystal and Bozzok after Blind-Eyed Pete sold them out so that he could restore his sight.
He also befriended Lord Shojo's cat, Mr. Scruffy, who he is very protective of. After he realized his former associate Buggy Lou was planning to eat Mr Scruffy, he immediately killed him. Likewise, Mr. Scruffy chose to assist him during a gladiatorial match, though he was capable of defeating his opponent by himself.
He also befriended an Allosaurus and used him to rescue Enor and Gannji, who he felt sorry for after Tarquin forced them to fight to the death, as they were both friends. He refused to abandon the lizard after he was polymorphed by Miron Shewdanker.
According to the Oracle, he will die by the end of the year.