The Darksaber. Tarre Vizla, the first Mandalorian Jedi, created this special lightsaber. Nobody knows why the blade has those strange patterns, but we all know that weapons are the Mandalorians' specialty. This is all original art, not traced or copied.
The Darksaber has passed through many hands, including Pri Vizla, Darth Maul, Sabine Wren, and Bo-katan Kryze. It has most recently fallen into the hands of the Empire, but I don't want to spoil for those who don't know what I'm talking about, so I'm asking that no Darksaber theories be shared in the comments.