Some cosmic entity or other decides to make you the Earth’s only superhero.
You get to select 3 DC characters to get your skills, powers, and abilities from before you go to work.
Remember you are alone in handling everything and not guaranteed to be welcomed by everyone. Not to make this too hard, you can ignore weaknesses.
Martian Manhunter, Superman with shape shifting & telepathy
The Engineer, Sometimes a show of force is better than actual force.
Lex Luthor, might need to think my way around some things.
Feel free to get your characters from comics, TV, film, or games.