Doug

Mike is an ex-boyfriend of Penny's. ("The Nerdvana Annihilation")

Penny broke up with Mike after he posted "details about their sex life" on his blog. She attempted to reconcile with him after Leonard unintentionally convinced her to do so, only to walk in on him having sex with another woman. After these events, Leonard took his chance and asked Penny out on a date. ("The Porkchop Indeterminacy")