We cannot conclude any particular people to be scientists comparable to Einstein or Newton, but there are some names in 3D printing industry who invented specific processes; they can be considered as pioneers in the field.
To name a few: Selective Laser Melting (SLM) was invented by Dr. Wilhelm Meiners, Dr. Konrad Wissenbach and Dr. Andres Gasser of Fraunhofer ILT, Germany. Dr. Carl Deckard and Dr. Joe Beaman from University of Texas at Austin invented Selective Laser Sintering (SLS). Stereolithography was founded by Japanese researcher Dr. Hideo Kodama, but the name ‘stereolithography’ was coined later by Chuck Hull, founder of 3D Systems Inc. Fused Deposition Modeling (FDM) was developed by Scott Crump, co-founder and chairman of Stratasys Ltd.
There are some conflicts with respect to the names as similar non-commercialized processes were developed much earlier, but the above mentioned people are the most recognized pioneers in 3D printing.