Klaus Ernst is a German politician and was a leading member of the Labour and Social Justice Party, later The Left and switched to BSW in October 2023.

The Left, commonly referred to as the Left Party, is a democratic socialist political party in Germany. The party was founded in 2007 as the result of the merger of the Party of Democratic Socialism (PDS) and Labour and Social Justice – The Electoral Alternative. Through the PDS, the party is the direct descendant of the Marxist–Leninist ruling party of former East Germany, that being the Socialist Unity Party of Germany (SED). Since 2022, The Left's co-chairpersons have been Janine Wissler and Martin Schirdewan. The party holds 28 seats out of 736 in the Bundestag, the federal legislature of Germany, having won 4.9% of votes cast in the 2021 German federal election. Its parliamentary group is the second-smallest of seven in the Bundestag, and is headed by parliamentary co-leaders Heidi Reichinnek and Sören Pellmann.