The Big Bang Theory has a habit of bringing characters into the fold with fans expecting them to play a large part, before dropping them without warning. One of the key examples is Alex, Sheldon's assistant for a spell at the university who vanished from the show. She flirted with Leonard during Season 6, causing a stir with Penny. She then filed a sexual harassment complaint about Sheldon after the flawed scientist made several remarks and displayed a book of STIs to divert her attention away from Leonard, but soon after she simply disappeared. We'll probably never see her again... Right?