The fan theory that DC's Joker was actually Robin has been a favorite amongst the comic book community, but Suicide Squad has now called it all into question.
In the beginning of the film, a short scene highlighting Harley Quinn's backstory is featured along with a list of crimes for which she's most infamous — one of them being her involvement in the murder of Robin, Batman's sidekick and best friend.
Prior to the new development, a convincing case had been made that Jared Leto's Joker was in fact the second Joker to have existed in the DC extended universe, originally having been Robin. A mixture of things led to the intriguing theory, including Leto's Joker's somewhat "damaged" appearance, the characters' similar ages, as well as a scene in Batman V Superman in which Robin's suit had been spray-painted with the phrase "Hahaha Joke's on you Batman."
Most convincingly, in 2000's animated film Batman Beyond: Return of the Joker, the plot centers around the Joker kidnapping Robin and torturing him until he adopts the identity of a "Joker Junior." In it, the Joker dies as Batman attempts to rescue Robin, but Robin is never quite the same afterward. So, as the theory went, Suicide Squad's Joker was this deranged version of "Joker Junior."
His looks certainly fit the bill unlike any other.
But unless the flashback detailing Harley's involvement in Robin's death was meant specifically to throw fans off, that theory has officially been debunked.
Hey DC sleuths, it was great while it lasted.