Steve Chow, better known by his YouTube username as BlackPenRedPen, and also as Teacher Chow (曹老師, Mandarin: Cáo, Min Nan: Chô) is a YouTube star and professor at Pierce College in Los Angeles^[1], who runs a channel where he posts videos of himself solving mathematical problems, with a focus on calculus and solving integrals. He is known for having a number of characteristic catchphrases, such as "I don't like to be on the bottom; I like to be on top", when moving the imaginary unit number from the bottom to the top of a quotient expression.

The name of the channel comes from the colors he prefers for whiteboard markers in many of his videos, and as time went on and he progressed to more complex problems and other colored markers began to be necessitated, it became something of a running joke.