In 'Coven', he played Kyle Spencer. This character was created in a rather unusual way. Evan Peters managed to capture Kyle's confusion and his new - found identity in a world full of witches. His acting added depth to the character, making Kyle an important part of the coven's story.
Evan Peters has appeared in multiple seasons of American Horror Story, including Murder House, Asylum, Coven, Freak Show, Hotel, Roanoke, Cult, and Apocalypse.
Yes, Evan Peters left American Horror Story. This could be due to his wanting to explore different roles and projects outside of the show or perhaps changes in the show's direction that didn't align with his interests.