Tang is an energy drink formulated by General Foods. It was touted as a breakfast drink when it came out. Consumers were not enthusiastic about it, until NASA started using it on its Gemini flights. Sales started picking up once the public started associating Tang with the astronauts. Now, Tang is available in 30 different flavors, and is owned by Kraft Foods.

The original orange flavored Tang was made in 1957 and the first powdered form was available in the market by 1959. Nowadays, Tang contains many artificial sweeteners, like Sucralose and Neotame. Also, Tang is available in much more concentrated form. Yes, it has changed a lot, to keep up with the changing expectations of the public.
And, Tang is also being touted as a dishwasher cleaning agent by consumers (of course, Kraft Foods does not recommend it!).
So, who invented Tang?

One thing which is certain is that, the inventor of Tang worked at General Foods (obvious)! And, multiple people may have been involved in the invention of Tang.

One of them is William Bruce James, a chemist who worked for General Foods. He also invented several Jell-O flavors. Another person who was involved with the invention of Tang is William A. Mitchell, who also invented Pop Rocks. William Mitchell has been involved with around 70 patents. These two seem to be the key people involved in the invention of Tang, according to the available information.