self-insert

A character in a story who represents the author's own person.

[Joss Whedon] loves sexualizing her, like […] making her fall for his self-insert Bruce Banner.

A character in a story who the reader/viewer is meant to identify with.

The female character has to be likable. She's a self-insert for the female viewers so she probably won't be unique, but watching her interact with other characters can't be frustrating.

To insert oneself.

For centuries, the commonest forms of implant had either been grown in situ or were designed to self-insert painlessly via existing orifices […]

To insert something into one's own body.

In Oregon, a group called Ceek Women's Health has begun clinical trials for a series of new devices—including […] a speculum that patients can self-insert.

To insert one's own person into a story as a character.

The character looks like Goldman and is voiced by him, so critics said he was self-inserting himself into a romantic situation with an underage character.