Taxonomy was simple when I was growing up. There were plants (which included bacteria) and animals, and that was it. Then things started splitting. The fungi got their own kingdom. Then the bacteria. Then it got crazy, with domains and supra-kingdoms and kingdoms, with the broader name "domains" assigned to the bacteria, the archaea, and the eukaryotes (which includes all the plants, animals, protists, and pretty much everything else most people have ever heard of). The only thing we knew for sure is that we at least had specimens belonging to all the kingdoms on up, even if we didn't have all the species.
For more than a century, there were a few microbes kicking around collections that were described by species names and sometimes grouped as a phylum (the level below kingdom) but didn't fit very well with other microbes. Now we know why: they weren't even in the same kingdom as anything else. Two new species picked up on a Canadian hike by graduate student Yana Eglit provided her and fellow scientists with their first look at living hemimastigotes, and they were so weird there was nothing else to do except give them their own supra-kingdom. As they wrote in Nature (the world's most prestigious scientific journal - heavy stuff for a grad student!) "The previous ranking of Hemimastigophora as a phylum understates the evolutionary distinctiveness of this group." The authors' findings "place Hemimastigophora outside of all established eukaryote supergroups. They instead comprise an independent supra-kingdom-level lineage..."