What changed because of them
US patent 454,622, filed 1891: a resonant transformer with an air core, driven at its own frequency. That is the device the whole hobby is named after, and every card here, SSTC, DRSSTC and QCW alike, is a way of driving it with parts he never had. Nothing on the tree descends from him by schematic; all of it descends from him by idea.
At Colorado Springs in 1899 he ran the magnifying transmitter, a three-coil system whose discharges he reported at over a hundred feet, from a laboratory powered off the local alternator. The photograph of him seated under the arcs is a double exposure, which he said so himself; the arcs were real, the sitting was not. The hobby has been arguing about his numbers ever since, which is the most respectful thing it can do with them.
A real legend, in the plain sense of the word: the one builder on this page everyone has heard of. His card is the root of the SSTC tree, a century before the next one. The portrait is the forum's own sticker of him, lightbulb and all; the photographs are his, long out of copyright.
Their boards
Colorado Springs, 1899: the magnifying transmitter (Dickenson V. Alley, public domain) 
portrait, about 1890 (Napoleon Sarony, public domain)
Builds and boards on the tree
Sources
Written from what Nikola Tesla published, by one person, so it can be wrong in places. The page is meant to become editable, wiki-style, by profiles above a trust level. Until then, corrections go to the forum, and anything Nikola Tesla asks to change or remove is changed the same day.