Jason Todd is the Joker is a DC fan theory, specifically concerning the events in the DC Extended Universe. This theory suggests that the version of The Joker seen in Suicide Squad is actually the cinematic adaptation of Jason Todd.
In the comics universe, Jason Todd became the second character to take the Robin identity. For 1988's "Batman: A Death in the Family" storyline, DC Comics held a telephone poll to determine whether or not the character would die at the hands of the Joker, Batman's nemesis. He was killed off by a margin of 72 votes (5,343 for, 5,271 against). Multiple comics after dealt with Bruce Wayne coming to terms with his death. However, he was later resurrected in the 2005's "Under the Hood" story arc, becoming the second character to take up the Red Hood alias and assuming a new role as an antihero who resembles Batman in many ways, except with a willingness to use lethal force and weapons.
- The Robin suit seen in Batman vs Superman is confirmed to be Jason Todd. 
- The Joker has notch-like scars in his shoulders that reflect the damage to the Robin costume.
- The Joker has a "J" tattoo underneath his eye. This resembles the scar that Jason Todd has in the Injustice video game.
- Other cryptic body art includes what appears to be a few feathers, possibly a robin on the Joker's right bicep.
- In one scene in Batman vs Superman, Bruce Wayne says: "20 years in Gotham. How many good guys are left? How many stayed that way?". Many fans believe that this is alluding to Jason Todd.
- The ages of the actors who play The Joker and Batman are both around the same age. Jared Leto is born in 1971. While, Ben Affleck is born in 1972. Jason Todd should have been a child while he was Robin. However, the ages of the actors don't match up for this to occur. Unless, the ages of the characters in-universe have been changed.