From RHJunior Comics Wiki
Morty is the goblin who imprinted on Ben's negative emotions - his doubts, guilt, fears, despair, and "the constant knowledge of your own inevitable death" (Morty's own pre-retcon words.) In the pre-retcon confrontation with the Evil Clown, Morty also describe himself as Ben's guilty conscience, who's job it was to protect Ben from from his temptations and "old nature".
Morty wears a slightly beaten-up top hat. He tends to keep his wings wrapped around himself like a cloak unless he's actively employing them.
In the pre-retcon version of the webcomic, called Under the Lemon Tree, certain facts were stated that have not so far been repeated, changed, or made irrelevant in the currently posted version. These include: