This amazing human being is...
Samuel L. Jackson
You wouldn't call your friends the way he's called,
This might have something to do with the fact that he's nearly always referenced with his full name including a middle initial, while you would typically not spend so much time with your friends' names.
Yet you envy him in his lab.
Possibly a reference to his part in Deep Blue Sea, which takes place in a sea lab, or as chief engineer in the Jurassic Park computer lab.
He maybe had many various jobs,
This guy is a seriously prolific actor and has played just about every part under the sun.
But purple isn't a good sign for him.
Not sure about it not being a good sign, but his favorite color is purple and often requests props of this color. Of particular note is Mace Windu of Star Wars, who wields a purple lightsaber.
he's the shepherd of us all, from weaks to heroes,
Shepherd refers to the infamous monologue from Pulp Fiction where he quotes Ezekiel 25:17 and ends with, "I’m tryin’ real hard to be the shepherd." From weak[ling]s to heroes possibly refers to his part in Unbreakable where he plays the fragile villain Mr. Glass opposite Bruce Willis's hero character.
Even if he is just a detestable servant.
Likely a reference to his character in Django Unchained.