I had thought Soo Bahk Do was Moo Duk Kwan. Also, I heard that Tae Kwon Do is/was?
That is correct, as JW said, Soo Bahk Do is THE Moo Duk Kwan, i.e. the Hwang family (H.C. Hwang, President of the US Soo Bahk Do Federation) is the creator and owner of THE Moo Duk Kwan.
As for Tae Kwon Do, there are in fact TKD schools which are Moo Duk Kwan style TKD schools. But they are not THE Moo Duk Kwan, nor are the affiliated with the US SBD Federation.
I'm sure that you can find much more in depth details on this history on this site....but basically....
Following the Japanese occupation of Korea (ended on 15 August 1945), 9 major Kwans or schools emerged. These were:
Song Moo Kwan
Han Moo Kwan
Chang Moo Kwan
Moo Duk Kwan
Oh Do Kwan
Kang Duk Kwan
Jung Do Kwan
Jido Kwan
Chung Do Kwan
As you know, Tang Soo Do and Soo Bahk Do are descended from the Moo Duk Kwan, but some other styles also descended from Moo Duk Kwan. Each of these Kwans graduated a great deal of black belts in those styles, some affiliated themselves with the stronger Kwans, some continued in their own styles.
Today, though, Soo Bahk Do (Tang Soo Do) and Tae Kwon Do are the only major Kwans remaining. Tae Kwon Do the more popular strains, as I understand it, are descended from the Oh Do Kwan, although I personally know a few practitioners from the Jido Kwan (also Tae Kwon Do).
Most KMA practitioners are descended from one of these Kwans in some way.