Apple named Jeff Williams as its chief operating officer Thursday, a job that hasn’t been filled since Tim Cook left the position more than four years ago to become CEO.

Williams has worked at Apple for about 17 years and supervised the launch of the Apple Watch, which went on sale earlier this year.

The company said he played a “key role” in the launch of the iPhone.

Apple also announced Thursday that it hired Tor Myhren from advertising company Grey Group to be vice president of marketing communications. He will start early next year and will oversee Apple’s advertisements, websites and product packaging. At Grey, Myhren was chief creative officer and president of its New York office.

Apple Inc., based in Cupertino, California, also expanded the roles of two other executives.

It upped Johny Srouji’s position to senior vice president of hardware technologies from vice president and said Senior Vice President of Worldwide Marketing Phil Schiller would now add Apple’s app store to his responsibilities.

In afternoon trading, Apple shares slipped $1.95, or 1.7 percent, to $109.39.

First Published December 17, 2015, 8:18 p.m.