Otto Rehhagel (born August 9 1938 in Essen) is a German football coach and former football player.

Rehhagel played for the local club Rot-Weiss Essen (1960-63), after the start of the Bundesliga for Hertha BSC Berlin (1963-65), and until 1972 for Kaiserslautern. He played 201 games in the Bundesliga.

He started to become a coach in 1974, and after several short assignments he worked for Werder Bremen from 1980 till 1995. He led his team to two German championships and two wins of the German Cup, as well as one win in the Cup Winners' Cup.

After less than one year for Bayern Munich he coached Kaiserslautern 1996-2000, winning a sensational German championship directly after rising from the 2nd league.

In 2001 he became coach of the Greek national team. The team reached the playoffs of the Euro 2004 cup, and sensationally reached the finals of the main tournament, defeating the defending champion France in the quarterfinals and the favored Czech Republic in the semifinals. Greece's fairytale run through the tournament concluded with a 1-0 victory over hosts Portugal in the final. Rehhagel, who was seen as the man most responsible for the team's success, became the first foreign coach ever to win a European Championship.

After Rudi Völler resigned as Germany coach in the wake of that country's first-round exit in Euro 2004, Rehhagel was considered by many to be a strong candidate for his homeland's job. After three other candidates removed themselves from consideration, Rehhagel received an offer to take over as Germany coach, which he officially turned down on July 10.

In Greece, he is occasionally called King Otto (βασιλιάς Όθων), probably in allusion to King Otto of Greece, however he already had this nickname during his coaching career in Germany. As a wordplay referring to Herakles, son of Zeus, he has been nicknamed "Rehakles" as well.