The pancake holster design is generally credited to Roy Baker, 1960's. The originals featured generally rounded shapes, very distinctive when compared to anything previously available, and had minimal form-fitting resulting in a generally flattened appearance.
Just about every holster maker has since offered some variation on the theme and a great deal of variety is now available. It is probably more accurate now to refer to these as being of pancake-style construction; i.e.: an inner panel and outer panel joined together to form a holster pocket with belt attachment points on either side of the handgun.