The Star Skinned Alchemists

The star skinned alchemists - also known as the Anunnaki, nephilim, deities, angels, demons, etc. - were the original alchemists that came and spread knowledge of Alchemy to magic and nonmagic kind alike. Capable of trasmuting without a circle or any ingredients, they are very powerful alchemists. Sometimes they take on the appearance of humanoid people with wings or horns or even human/creature hybrids or various other combinations.
Because their skin holds the traced constelations of the night sky under which they were born, they are their own planetary alignment. Since they live considerably longer than humans, though are not immortal, many cultures saw them as deities. Often times, their descendants would be a mix of human and Anunnaki, being given the name Nephilim. Though the nephilim were still powerful, they were considerably less powerful than the Anunnaki themselves. The humans even less so, though there were a few fairly talented humans.
There were, in recorded history, only a small handful of non-Anunnaki that were granted the power of the original Alchemists. This came in the form of a philosopher's stone. A philosopher's stone is a stone made of the blood of an Anunnaki. This is the very substance that allows them to create, deconstruct, and perform alchemic transmutations so easily.
The blood of the Anunnaki is mixed with the user in question to form a chrystalized stone, as well as make it impossible for anyone else to use the stoneaside from the two whose blood it contains. Merlin was one of these users granted a philosopher's stone. Moses was another alchemist permitted this honor.

Notes on Anunnaki: They are not angels but they have me, worked with, and mixed with angels.