Johannes Haag is a German actor and voice actor born in 1965 in Husum, Nordfriesland, though some sources list his birth year as 1960. He completed his acting training at the Margot Höpfner Schauspielschule in Hamburg and passed the state examination through Ida Ehre. His early career included stage engagements at the Landestheater Schwaben in Memmingen, followed by work at Kampnagel in Hamburg, the Altonaer Theater, the Landesbühne Hannover, and the Ibsen Tourneetheater Hamburg. He spent two years in Amsterdam with the theater group DESIREE, a collaboration that produced work at the Theater am Halleschen Ufer in Berlin and the Theater Bellevue Amsterdam. He was also a longtime member of the Hamburger Art Ensemble, performing in Der Hamburger Jedermann for twenty-five years. Since 1999, he has lived and worked in Munich, appearing on stages such as the Blutenburg Theater, the Stadttheater Ulm, the Teamtheater Tankstelle, and the theater UND SO FORT.

As a voice actor, Johannes Haag has contributed German dubbing voices to numerous anime and international live-action productions. He is known for providing the German voice of Kishward in the anime series The Heroic Legend of Arslan from 2015. His extensive work in the long-running series One Piece includes voicing several characters, such as Sai in his second voice role from episode 640 onward, Yamakaji, Bizarre, Fossa, and Avalo Pizarro. He also voiced Iris's uncle in the anime series Violet Evergarden. Beyond anime, his dubbing portfolio includes roles in live-action television series such as The Blacklist, The 100, Bosch, Jane the Virgin, Code Black, and Outlander. His film dubbing work includes roles in The Ballad of Lefty Brown, Archive, and Shock and Awe - Krieg der Lügen.

In addition to voice acting, Johannes Haag has maintained a parallel career as an on-screen actor in German television. His credits include appearances on series such as Siska, Ein Fall für zwei, Hubert und Staller, Die Rosenheim-Cops, and Watzmann ermittelt. His career has been characterized by consistent work across both stage and screen, as well as in the dubbing studio, with significant activity in the German dubbing industry for anime productions.