Lieutenant Von Smittelhoffen is a fictional German army soldier, a small character in the series Allo Allo. At some point the name was assumed by Denise Laroque about Rene Artois in disguise as a German lieutenant.
It is suggested that Von Smittelhoffen is either a name made up or a "real" German soldier assumed by Rene, but never actually seen on screen. The latter is supported by Denise Laroque when she mention this name after having captured and interrogating a soldier (Rene Artois) wearing a German lieutenants uniform. It is assumed that the uniform carried some sort of identification of Von Smittelhoffen.