Michael B. Jordan kept a diary based on his Black Panther character, Erik Killmonger, making entries before filming began

Jordan stopped by The Late Show with Stephen Colbert on Tuesday and told the host he plots a backstory for every character he plays.

“We write a backstory,” he said. “I have diaries for every character that I have. From the earliest memory up until the first page of the script.”

Jordan, who’s promoting his new HBO film Fahrenheit 451, said Killmonger’s journey was much darker than than that of his other characters.

“It was deep, and it allowed me to go to that place right before a scene,” the actor told Colbert. “It allowed me to lock in.”

Check out the video below.