Last Dark One

The Last Dark One is the last of the Desert Muck Leech species, as well as all the species that were considered to be part of the Dark Ones. It originally lived in a puddle on Mars, but was taken out of its habitat and the rest of its species were wiped out by Leo Wong to make room for a parking lot in the second Mars Vegas. Turanga Leela kept the leech as a pet, and it later became the mascot for the Feministas.

Leela allowed the last Dark One to survive on her blood until the Feministas were sent to Maxi-Padlock, a women's prison, where it was used at a breakout attempt by eating a hole through the wall. The breakout failed, but they were rescued by Bender.

It was taken to the ceremony for the implosion of the violet dwarf star, where it revealed itself to be the last Dark One, after taking a hit from the Omega Device. It managed to kill Hutch Waterfall before getting killed by The Last Encyclopod. Its corpse was eaten by Zoidberg before the Encyclopod had a chance to preserve its DNA, thus making it the very last of its species and the last casualty of the evolutionary arms race.

Trivia

 * The Last Dark One is the main villain of Into the Wild Green Yonder.
 * It is revealed in the comentary of Into the Wild Green Yonder that Maurice LaMarche's animal voice for this character had to be computer-altered in order to make it sound smaller.