Gerhard III of Holstein-Rendsburg (c. 1292 – 1 April 1340), sometimes called Gerhard the Great, and in Denmark also known as Count Gert or den kullede greve ("the bald count"), was a German prince from the Schauenburg family who ruled Holstein-Rendsburg and a large part of Denmark during the interregnum of 1332–40.

In 1325 Gerhard began his career in the North by taking over the guardianship for his minor nephew Duke Valdemar of Schleswig.

From 1332 to 1340 Count Gerhard was the real ruler of what had been Denmark, being the lord of both Jutland and Funen, leaving the rest of the country to Johan.

Gerhard seems to have prepared to compromise in return for his outstanding debts being dealt with but before a solution was reached in the spring of 1340 he started a new campaign against rebels in North Jutland.

During the campaign, he was slain in the town of Randers by the Danish squire Niels Ebbesen who had entered his bedroom together with some of his men.