Have it in the background.

I don't think people are entitled to reading a massive wall of text to prove "look! I make an in depth character!" You show the depth of a character by roleplaying them. Let the characters speak for themselves in regards to depth. Speaking for myself, I see no merits to appeasing someone who thinks depth is the ability to make a wall of text detailing all the things they have done (and I don't consider depth to be a superhero who destroyed 200 demons in detailed ways, by the way, as an example).

A character with a relatively boring life and background that is presented well can have considerably more depth than an emo megamaniac supermage with a hundred powers and dozens of world-saving achievements.