He's wearing the traditional ceremonial warrior hat of his people.

There were several members of this species who fell to the dark side because the Jedi thought that they could never be Force-sensitive and didn't go out and look for recruit, so they never learned how to use it properly. Elvory wants to spread knowledge about the Force so this doesn't happen anymore. He was only discovered by the Jedi because he was born on Coruscant.

When he went to get a kyber crystal as a kid, he never found a crystal that spoke to him and he returned home feeling lonely and inadequate. As a teenager, he built this lightsaber from a crystal which he took from a dark side user he defeated on his species' home planet.

His tail got cut off in a battle. Sometimes he wears a mechanical tail for better balance.