In this case, it's Charles Hinton, who from his Wikipedia entry was: a British mathematician who was interested and wrote about higher dimensions, particularly a fourth dimension of space, and is known for coining the word tesseract and for his work on methods of visualizing the geometry of higher dimensions.
Also from that entry:
In an 1880 article entitled "What is the Fourth Dimension?", Hinton suggested that points moving around in three dimensions might be imagined as successive cross-sections of a static four-dimensional arrangement of lines passing through a three-dimensional plane, an idea that anticipated the notion of world lines, and of time as a fourth dimension (although Hinton did not propose this explicitly, and the article was mainly concerned with the possibility of a fourth spatial dimension), in Einstein's theory of relativity. Hinton later introduced a system of colored cubes by the study of which, he claimed, it was possible to learn to visualize four-dimensional space (Casting out the Self, 1904). Rumors subsequently arose that these cubes had driven more than one hopeful person insane.
Hinton created several new words to describe elements in the fourth dimension. According to OED, he first used the word tesseract in 1888 in his book A New Era of Thought. He also invented the words "kata" (from the Greek "down from") and "ana" (from the Greek "up toward") to describe the two opposing fourth-dimensional directions—the 4-D equivalents of left and right, forwards and backwards, and up and down.
Charles H. Hinton (1853-1907) of Princeton University, University of Minnesota, and US Naval Observatory