Mr. X is a villain in Saints Row IV, who appears in the mission "The Case of Mr. X".
At the start of the mission "The Case of Mr. X", Asha Odekar and The President search for Mr. X. After Asha and The President bypass all of the guards, Mr. X shows up in a monitor and taunts Asha by killing a virtual copy of Matt Miller right in front of her and insults Johnny Gat by saying he cried like a like a little bitch when his girlfriend Aisha died. The real President shows up and says "Then you are gonna fuckin love me you piece of shit". Then Mr. X sounds the alarm and sends their men, Masako and the Murderbots to attack Asha and The President. When they reach Mr. X, Asha and The President battle Mr. X until Mr. X is killed by the President.
- Mr. X's eye patch is a reference to the character Big Boss in the Metal Gear Solid series. It's also possible that the goatee is a reference to the Star Trek episode, Mirror, Mirror, where Evil Spock is shown to have a goatee.
- Strangely Mr. X will still have a goatee even if they are Female.
- The final confrontation against Mr. X bears a resemblance in dialogue and gameplay to the final confrontation in Syphon Filter: Dark Mirror.
- The boss fight combines elements from Sniper Wolf and Vulcan Raven boss fights from Metal Gear Solid. Sniper Wolf shoots Snake with a sniper rifle from a far-away area, switching between cover positions, and Vulcan Raven boss fight area has several large crates that provide cover from enemy fire.
- Even if the Protagonist is a female she will still be called Mr. X
- The cigarette box Asha picks up from Mr. X's corpse has several Saint's fleur-de-lis symbols on it.