Doomsday is an incredibly powerful monster with regenerative abilities. Each time he dies he respawns having evolved past the last thing that killed him, making him slowly invulnerable over the course of centuries traveling the universe. Developed as a weapon in a facility by the scientist Bertron, he was tested out through many of his first deaths on the planet Krypton, giving him an immense natural hatred towards Kryptonians.
Batman v Superman: Dawn of Justice Thought it was pretty good actually. Very pretty film. It wasn't perfect but still entertaining. Only criticism is that one particular turning point in the film seemed to be over very quickly!