The Megans were extradimensional shapeshifting beings with strong psionic and telekinetic powers.They, along with the Olympians, the Preservers, the Danons and the Furies, had once visited Earth, inspiring legends about demons, devils, satyrs and witches.
By the 23rd century they had largely withdrawn from the Milkyway galaxy into another parallel-dimension, though some still visited the galactic core.
Doctor Brelkin Iser had theorized that the Megans actually had been a spliter group or rogue faction among the Olympians, descendants of the Progenitors and directly related to the ancestors of the Q.