The 30-year-old was signed from Olympique Lyonnais for €28 million by Mourinho in 2005 - a then-club record fee - after a long-running pursuit, making nearly 100 appearances in all competitions before the manager left the club in September 2007.
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"He's a lovely man. When you work with him and get close to him you understand the kind of person he is," Essien told his official YouTube channel.
"He gives everything and he is very friendly. It's funny how some people see him when he is giving interviews, but he is a lovely man.
"I think he has got what most managers don't have. He is very close with his players, always trying to get the best out of his players and talking to his players.
"He knows when you aren't doing well and tells you, so you do well in the next game. You have to keep fighting."