When the MASTR series of equipment was first introduced, they were the first GE-PRS products to be SOLID STATE.  (A very big deal in those days.)  This name was created by the following gentlemen: Dick Buesing, Bob Giorgi and Phil Dellwo.

The MASTR Series replaced the TPL Series (or Transistorized Progress Line).

Source:
Mark A. Cobbeldick   KB4CVN