Jens Böhrnsen (born 12 June 1949 in Bremen) is a German politician of the SPD. From 2005 to 2015, he served as the President of the Senate and Mayor of the Free Hanseatic City of Bremen, that is, the head of government of the city-state of Bremen. He became President of the Federal Council in 2009, and as such, he was acting head of state (31 May - 30 June 2010) following the resignation of German President Horst Köhler .