What is the relationship between Tim Cook and chief executive officer in the context of the input sentence. Choose an answer from: product/material produced; manufacturer; distributed by; industry; position held; original broadcaster; owned by; founded by; distribution format; headquarters location; stock exchange; currency; parent organization; chief executive officer; director/manager; owner of; operator; member of; employer; chairperson; platform; subsidiary; legal form; publisher; developer; brand; business division; location of formation; creator.

While chief executive officer Tim Cook has succeeded in introducing an entirely new category with the Apple Watch, sales remain modest, indicating that Apple will have to keep relying on the iPhone to fuel growth.

Answer: position_held