The Nikon F is an early 35mm SLR with a pentaprism. Professional SLR’s go back to the 19th century. For example Graflex. http://camera-wiki.org/wiki/Graflex_reflex_models
Here is Dorothea Lange with a Graflex SLR. https://www.shorpy.com/Dorothea-Lange?size=_original#caption It may even be the camera she used for Migrant Mother.
Prior to the Nikon F there were 35mm SLR cameras with other types of finders, e.g. waist level.
Hasselblad produced its first consumer SLR’s in the late 1940’s and the iconic 500 series was launched two years prior to the Nikon F (1957 v 1959). https://www.hasselblad.com/inspiration/history/first-consume...