Arco Blathereen was an obese Raxacoricofallapatorian, and the patriarch of the Blathereen family in the 26th century. After he hid in a toxic dump while being hunted by the authorities, Arco could only breathe in poisonous gas.
Arco was behind the plan to turn the Justicia system into a massive flame-thrower, to burn other planets and sell the remains as fuel.
He was foiled and killed by his half-sister Ermenshrew Blathereen for giving in to the Ninth Doctor's demands so easily.
After the Blathereen were defeated, the last survivour requested that Arco's body be cremated. However the Blathereen leapt into the flames and vanished, along with Arco's body. It was later revealed that Arco's body was used by Ecktosca Fel-Fotch Heppen-Bar Slitheen to hide and, with his Aunt Callis Fel-Fotch Heppen-Bar Slitheen (who was in the body of the Blathereen survivor), escaped the funeral pyre by teleport. (PROSE: The Monsters Inside)