Trickster noun – A dishonest person who uses clever means to cheat others out of something of value. Betrayer and trickster are semantically related. Sometimes you can use "Betrayer" instead a noun "Trickster". Nearby Word: trick
It's often believed in the scholarship of Norse Mythology that Loki was the pretty standard Trickster Archetype found in about half the tales, not the sudden betrayer of the gods/Satan analog that shows up partway through Snorri Sturluson's writing.