Buppido

Buppido is a character from the Dungeons and Dragons campaign, "Out of the Abyss" and while he can be introduced as an NPC that adventurers can interact and befriend he inevitably becomes a betrayer and an enemy, this is in-keeping with the generally unpleasant nature of the Derro themselves (who are largely a chaotic evil society within the Dungeons and Dragons multiverse).

History
Buppido was a Derro of some age who originated from the city of Gracklstugh but took to wandering the Underdark, undertaking in methodical and ritualistic killings - befriending his victims and gaining their trust under a friendly guise before murdering them in a fit of insanity.

Despite his dangerous nature he would become a prisoner of the Drow slavers of Velkynvelve and is thus introduced to player parties as one of the many slaves they share a cell with and may take with them when they escape.

Inevitably Buppido will latch onto one of the party and try to befriend them, only to very likely trick them into an attempt on their life - what happens to him at this point depends vastly on whatever the player group or Dungeon Master may have planned but in general he either dies in combat or escapes in some fashion.

Personality
Buppido was insane and had a delusion that he was the living incarnation of Diinakarazan and an avatar of murder who must offer ritualistic sacrifices to spread carnage and inspire the chaos and evil of his own people.

When in a frenzied state he was fearless and believed himself invincible, he also believed that any setbacks were all part of his own "divine plan".

Despite his extreme insanity Buppido could also switch into a passive mode in order to befriend others and trick them into vulnerable positions, in this sense he was a calculating and brutally cunning killer despite his chaotic nature.