Maldis was a psionic entity that existed partially in the Prime Reality and partially in another realm of his creation. Maldis' psionic powers were so great that he had long ago evolved past the need for a corporeal body, though unlike many other non-corporeal entities Maldis still needed to feed. Maldis fed on life force itself, using pain, hatred, and fear to cause death and draw out the energy he needed for sustenance. In order to satiate his hunger, Maldis would enslave entire worlds until they were too downtrodden to fill his appetite -- at which point he would move on to other inhabited planets.
Seeking a means to enslave the Peacekeepers, Maldis lured John Crichton away from the rest of Moya's crew and then brought his soul into Maldis' realm. Then, Maldis brought Bialar Crais' soul into the arena, and set the two against each other. Though Crichton kept attempting to peacefully resolve their differences, the enraged Crais worked himself into a frenzy. When Crichton eventually got the better of his opponent, Maldis released Crais' soul. His plan, he explained, was to have lure Crais' command carrier to the planet where Maldis and Crichton had met. He would then enslave the command carrier and create death on a much larger scale. Before Maldis was able to kill Crichton, however, Pa'u Zotoh Zhaan intervened. Using Liko's energy, she was able to force Maldis into a corporeal form in his own realm -- this gave Crichton the opportunity to attack him and escape back to the Prime Reality.
Maldis was deeply weakened by this experience, and sought out opportunity to exact revenge upon the Delvian who had defeated him. Fortunately, he was able to create a small anchor to the Prime Reality through the form of Kyvan. Using considerable psychic power, he created a commerce station for Kyvan to inhabit. There, Kyvan gave a painting to Chiana. The painting was, in fact, a portal to Maldis' dimension which he used to "kill" -- or, in truth, kidnap -- each member of Moya's crew. Zhaan, having figured out what was happening, set in motion a plan with Aeryn Sun.
Zhaan allowed herself to be taken by the portrait, leaving instructions for Aeryn to destroy Kyvan. With both of these tasks accomplished, Zhaan confronted Maldis and occupied him long enough for her friends to escape the painting -- at this point, Zhaan herself escaped and lured Maldis out into the Prime Reality. Aeryn, in her Prowler, and several of Moya's DRDs opened fire on the portrait -- destroying it and weakening Maldis even further.
Maldis is derived from Farscape.