2013/14 Italian Serie A
In 2005, Chelsea fought off stiff competition from Manchester United to pay £24.4 million for a Ghanaian central midfield with a fine reputation after some outstanding performances for Lyon - but few could have predicted just how crucial Essien would become for the Blues.
He moved to France in 2001, joining Bastia from Liberty Professionals, and reached the French Cup final in his debut season before joining Lyon, where two Championship medals and the 2004-05 French Players' Player of the Year award followed.
In his prime, Essien was a commanding figure in the middle of the park - a fearsome tackler but also able to drive the team forward with powerful runs. He has also shown great versatility, playing on the right-hand side of both defence and midfield.
Essien tasted success early in his career as he picked up a gold medal with Ghana at the African Under-17 Championships, a bronze medal at World Under-17 Championships and silver at the World Youth Championships. The midfielder made his full debut for Ghana at the 2002 African Nations Cup and helped the Black Stars reach the World Cup for the first ever time in 2006. Essien ruptured his cruciate ligament in a World Cup qualifier in September 2008, but after returning in March he has helped secure Ghana's place at the 2010 finals.
But Essien has struggled to recover from that knee injury and was injured again at the 2010 African Nations Cup final, an injury that cost him a place at the World Cup finals on African soil.
Essien picked up a second Premier League title in 2009-10, but injury restricted him to just 13 starts in the league, and he showed little sign of returning to his former self before being shipped off on loan in the summer of 2012 to Real Madrid and Mourinho.
Strengths: When at his best, his power, drive and relentless work-rate are phenomenal, and he also possesses an incredible shot from distance.
Weaknesses: His aerial ability has been a longstanding problem, but more significant now is that he looks to have been sapped of his power.
Career High: In 2006, he won the Premier League title with Chelsea and played for Ghana in their inaugural World Cup in Germany, as well as being nominated for the FIFA World Player of the Year award.
Career Low: Two years spent fighting knee problems, which forced him to miss the African Nations Cup and the World Cup in Africa in 2010.
Style: Combative box-to-box midfielder who likes to be involved with play at all times, whether in defence or attack.
Quotes: "Essien is one of the finest players in the world and will fit into any team. Any team will like to have such a talent in their set-up" - Ghana assistant coach Akwesi Appiah, May 2011.
Trivia: Essien's nickname is "The Bison" because of his powerful physical presence.
ITALIAN SERIE A