Dan is the Dread Demon from the game called Helltaker, a fan OC. He is known to use people as "test subjects" and test them with very strange things, such as syringes, that have unknown substance in it. It most likely might kill you. 
His expression and personality is rather insane when first meeting a human being. But in natural he is usually tired and bored like Pandemonica. 

His appearance? he has a long like dark cloak and underneath the cloak he has a red sweater.