The art teacher is a one-shot character who appears in the episode "Riley Wuz Here". His character is based on a famous American painter, Bob Ross. He allegedly served in the U.S. military during the Gulf War.
He is portrayed as a soft spoken, compassionate man who desires to help Riley improve as an artist. He first meets Riley after Riley spray paints "Riley Wuz Here" on the side of a house. He critiques the mural and helps Riley make it smaller so that the message is clearer.
After Riley gets into trouble for his spray painting, Robert decides to send him for art lessons with the Art Teacher. Riley is initially disinterested in what his teacher has to say, but once Riley shows improvement, the teacher decides that they should "move on to a bigger canvas" (i.e. spray paint houses).
After painting several elegant murals (a bowl of fruit and Ol' Dirty Bastard) on the sides of houses, the Art Teacher decides that Riley should paint a picture of someone he loves, preferably someone who has passed away. Riley complies and on their last night together, Riley paints a mural of his deceased parents, finally receiving the recognition he sought as an artist while having a profound emotional effect on his family.
The two are nearly caught by the police, but the Art Teacher and Riley speed off in their car. The police give chase, but the Art Teacher pulls out a gun and shoots out the tires on the cop cars, enabling their escape. The Art Teacher drops Riley back off at his house. Riley thanks the Art Teacher for helping him, and the Art Teacher thanks Riley in turn for being such a good student. He then drives off.