Johann Leo Weisgerber (25 February 1899, Metz – 8 August 1985, Bonn) was a Lorraine-born German linguist who also specialized in Celtic linguistics.
He developed the "organicist" or "relativist" theory that different languages produce different experiences.
He was son of a village-teacher who served as a young man in the German army in Flanders and could not return to his home city for that.
During World War II his pan-Celticist ideology was co-opted to support the German war effort, as did pro-Polish and pro-Czech ideology on the side of the allies.