I started reading a Chinese webnovel called 'The Dark King' on Wixianation.com and there is a character in the early chapters who is an alchemist. I based this concept in the description provided in the chapter, plus I added some of my own. This are some of the key words describing the character: Old man, tattered clothes, skinny limbs, left arm has attached a long snake, snake is as thick as a baby arm.
This character in the novel is an alchemist, and normally live in the shadows. In the novel alchemists are ''evil''. His purpose is to create the "Philosopher's stone" and get immortality. Due to his lack of strength he experiments on his body and attached a snake to his left arm. He uses this snake to attack from the shadows but it takes a toll to his stamina. He also knows how to create potions.
Disclaimer: This is not an official concept for the character, it is simply my own interpretation.