Despite all the praise Steve Jobs showered on protege Tim Cook, he did have one reservation — and it was a doozy.

"Tim's not a product person, per se," Jobs said, according to his new biography written by Walter Isaacson.

The fact that Cook isn't a product person isn't exactly a shocker, but it's an interesting detail considering Apple's rise over the last decade is entirely due to a string of great products from Jobs.

Cook will have to lean on other executives to help guide product development without Jobs.

More details on the relationship between the two men from the book:

Jobs called Cook a "cool customer" that was his good foil. Jobs was prone to temper tantrums and had an explosive personality, while Cook was cool and composed.

"What I learned about Steve was that people mistook some of his comments as ranting or negativism, but it was really just the way he showed passion," Cook said. "So that's how I processed it, I never took issues personally."