A series of
famous German Twin Lens Reflex cameras dating from their first release i 1928 (which used 117 film), the current design became more or less fixed in 1949 with the release of the 2.8A type 1, derivatives of which are still in
production in a
limited form today(although not worth the money these days when purchased new IMO).
The Rolliflex design could not be improved upon, and never really was (see Mamiya TLR for a damn good try), and in that it received a substantial amount of imitation (see Yashica TLR). Simple, beautiful, efficient and elegant are all words frequently attributed to a Rolleiflex.
Throughout the years there have been numerous Rolleiflex TLRs, all have incorporated excellent lenses that still get praised 30 years after they hit the shelves. The Zeiss Planar lenses tend to get more praise, although I've heard that the less expensive Xenotars were so good that very little difference could be noticed.
Nearly all Rolleiflex cameras use the 6cm x 6cm format, all post war (that would be WWII) Rolleiflex use 120 film with the newest allowing 220 film as well.
I give thanks to the Medium Format Digest for all research data.