Protean refers to Proteus, the mythologic master of disguise. According to the ancient Greeks, Proteus was the shepherd who looked after Poseidon's sea creatures. Proteus had the gift of prophecy. Determined not to share his knowledge, he changed his shape to avoid attention. The only way to learn what he knew was to sneak up behind him during his nap and hold him (while he frantically changed from shape to shape) until he revealed what he knew. Protean means as mutable and adaptable as the mythological shepherd.
For example, the ways in which AIDS may present are numerous, and thus, protean.