If you want a really enjoyable read about Karras, John Gordy and the Lions back in the 60's read George Plimpton's book Mad Ducks and Bears, when as an author he was allowed to attend the Lions training camp and eventually run a play in pre season.
I think I read this in 6th or 7th grade when my father gave me the book. It was the funniest thing I'd read to that point in my life. Until you read it you won't know what a prankster Karras was.
RIP dude, you were one of the greats.