Like other people said, "daimon" in greek is not the same as what the word got used for in christianity. And like Conon said, kakodaimons only became a notion in the era of gnostic religions (which were a mystical hybrid of ancient greek philosophy and "christiany" - in a very general sense - stuff).
Socrates famously spoke of his "daimon" who urged him to do things, like learn music. And like Morticia said, the pre-gnostic era daimons were basically lesser gods, which is why one of the accusations in the trial of Socrates was that he "introduces new daimons" (kaina daimonia).
The
Erinyes , aka "Zeus's winged dogs", can be seen as a type of what now is identified as demon. They were sent by the gods to punish anyone who committed hubris, and according to a nice aphorism by Heraklitos: "Not even the Sun can exceed what was allotted to him, for if he does then the Erinyes will find him and see that he faces trial".
The three
Gorgones (two of which were immortal; the third one was killed by Perseas) also look like demons in their vase depictions. While the Erinyes at times have nice-looking female forms, and at others are nightmarish, the two immortal Gorgones look like a strange ant in most depictions, and bearded horrible old women in others.
Although they aren't really interested in dealing with humans, and not even the gods can stand to look at them - much like with other monsters, like the Scylla, the "immortal evil".