Like every movement, RepRap has it's heros. People which did and/or do outstanding work. Thanks you guys, without you the success of the RepRap movement wouldn't have happened the way it did!
Ed Sells is the pioneer of usable RepRap printers, he designed the Original Mendel in 2009. His design was successful enough to be about the only recommended printer design for about a year and many more recent designs still reflect his ideas.
Alessandro is inventor and maintainer of slic3r, a really feature rich slicer for 3D printers, especially the RepRap models.