"He has a lot of experience," Koeman told the club website (www.evertonfc.com).
"He is an important player on the pitch but also important for his team mates and certainly the young players to show them what you need to do to reach that high standard of football.
"That means he needs to be a leader off the pitch and if I see how he's working and what he's doing with all the players it's really what we want."
The Merseyside club have been one of the most active Premier League clubs in the transfer window, with their major signings including Rooney, Jordan Pickford, Michael Keane, Davy Klaassen, Henry Onyekuru, Sandro Ramirez and Cuco Martina.
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With Koeman hoping to sustain a challenge in both the Premier League and Europe during the upcoming season, the Dutchman believes they have added plenty of quality to the squad.
"I'm really happy with how the new players have settled in," Koeman added. "They have great futures at Everton and provide the quality we need to improve."
Everton will begin their new season against Ruzomberok, of Slovakia, in the Europa League third qualifying round. Koeman's side will be at home in the first leg on Thursday with the return fixture scheduled on Aug. 3.
(Reporting by Hardik Vyas in Bengaluru; Editing by Ian Chadband)
