Who is Harrison Wells?

"Who is Harrison Wells?" is the nineteenth episode of the first season of The Flash and the nineteenth episode overall. It aired on April 21, 2015.

Synopsis
Joe and Cisco head to Starling City to continue their investigation of Dr. Wells. While in town, the duo enlists the help of Captain Lance, and Cisco meets the Black Canary, who asks him for a favor. Meanwhile, back in Central City, Barry races to catch a meta-human named Hannibal Bates who can transform himself into every person he touches – which includes Eddie, Iris, Caitlin and even The Flash.