TDC was short for the Three Dimension Company, which jumped into the stereo photography fad of the early 1950s with both feet. At some point they were purchased by Bell & Howell, but I do not know when.
Due to the fact that it was only briefly popular, most manufacturers only offered a single model (e.g. Kodak, Graflex and Revere. A few, like Sawyers, offered two. TDC and David White are the only ones I can think of which offered three.
The first two offerings were the Colorist and this Colorist II. They are essentially the same camera except that the Colorist II has a coupled rangefinder; on the original Colorist you have to determine the distance yourself. Both were made in Germany by Bodensee Kamerawerke.
TDC's third camera was the Stereo Vivid, which was made in USA, and is a comletely different camera and features layout. I believe the Vivid was made by the same folks who made the Viewmaster Personal.
One of the big differences between TDC and most other companies, like Kodak, is that they offered serious viewing accessories. David White, Revere, and Kodak all made hand-held viewers; TDC offered proper slide projectors so you could project them on a big screen and view them with polarized glasses. I've got both their big projector and their table-top viewer.