Klaus Wowereit (born 1 October 1953 in West Berlin) is a German politician, member of the SPD (Social Democratic Party), and has been the mayor of Berlin since the 2001 state elections, where he won a plurality of the votes, 29.7%. He served as President of the Bundesrat (the second highest office in Germany) in 2001/02. His SPD-led coalition was re-elected in the 2006 elections. He is also sometimes mentioned as a possible SPD candidate for the Chancellorship of Germany (Kanzlerkandidatur), though his chances diminished after his decision to enter into a coalition with the socialist Left Party for a second term.

Until 1973, Klaus Wowereit attended the Ulrich-von-Hutten-Oberschule in Berlin. Afterwards, he studied law at the Free University Berlin (State Exams, 1981 and 1984).

After 3 years as a civil servant in the Senate office of the Interior Wowereit stood for election as municipal councillor in Tempelhof borough. At the age of 30, he was therefore the youngest councilor in the city of Berlin. After eleven years as a Borough Councillor he stood for the Berlin House of Deputies (Abgeordnetenhaus von Berlin) which serves as the City's Landtag or state legislature in 1995. In December 1999, he was elected chairman of the SPD parliamentary group in the Abgeordnetenhaus. Since June 2001 he has served as Governing Mayor (Regierender Bürgermeister) of Berlin. Previously, the SPD had left the Grand coalition with the CDU and initiated new elections. After this election and following long-time negotiations, Wowereit finally started a coalition with the PDS.