Meglos is the last survivor of the Zolfa-Thuran race. He is a plant, and a xerophyte, looking much like a cactus when standing upright. He is not extremely mobile in his natural form, but does seem to be able to slither along the ground. When doing this, his spines presumably retract, causing him to appear more like a green slug.
By modulating himself on a particular wave of light, Meglos has the ability to transfer himself to another body - Earthlings seem to be particularly useful to him. His new host temporarily develops spiny warts, which soon fade except under moments of stress, when they may reappear. Meglos seems to abandon his ordinary body during this process, but he can regain it if he decides to extract himself from his host. While in the body of the host, Meglos can change his appearance, and even his voice, to resemble someone else. (He may only be able to do this by recording the appearance and voiceprint of another being on the computer in his laboratory.) The host can rebel, however, and attempt to escape Meglos' control. In these instances, Meglos' current appearance displays the same spiny warts until he is able to get his host body back under his control.
Meglos apparently lives in a sort of laboratory beneath the surface of Zolfa-Thura, surrounded by the five screens of Zolfa-Thura. Amongst other things, the equipment in the lab can create a chronic hysteresis - a fold in time, like an ever-repeating time loop - to trap people. When the dodecahedron is placed atop the building, the screens of Zolfa-Thura can amplify its energy and converge the resulting five beams on any point in the galaxy, thus completely destroying it. The other Zolfa-Thurans apparently destroyed themselves in order to prevent just such a thing from happening. Meglos himself was destroyed during his first attempt, when the Doctor redirected the energy back onto the planet of Zolfa-Thura.
