William Diller Matthew
William Diller Matthew FRS was a vertebrate paleontologist who worked primarily on mammal fossils, although he also published a few early papers on mineralogy, petrological geology, one on botany, one on trilobites, and he described Tetraceratops insignis, which was much later suggested to be the oldest known therapsid.
Biography from
Wikipedia, CC BY-SA 4.0. Portrait: via Wikipedia (see source).