Dennis O'Flannelry is a scientist, inventor, and Mark's best friend.
Dennis is intent on three things in life; building a mankind-saving invention, capturing a UFO for study, and eating pizza. When not in his lab (the basement of his Mom's house), reading comic books, or eating a slice of pizza, Dennis can most often be found discussing the finer points of philosophy and science with Mark... along with such topics as sci-fi, and new ways to foil the evil plans of the town grouch, Sherm Sherman!