Jaster Mereel was the Mandalore of the Mandalorian Empire from 3,949 BBY to 3,939 BBY. He was good friends with Mandalorians Rikenn Tarbann and Bage Nylos. Mereel disappeared during the Battle of Onderon in the Second Mandalorian Wars where he still remains MIA.
It was Jaster whom had started the war by attacking a non-hostile, rescue group of Jedi and Republic soldiers. Not much else is known about Jaster except he was an excellent tactician and had almost taken over the entire galaxy, the first Mandalorians to come so close.
In 35 ABY, Mereel was resurrected by Azeroth the Profit for his Army of Bounty Hunters. He was a formidable opponent but in 37 ABY, however, he was killed by Kalendor.
Behind the scenes[]
According to the creator of the fanon character Jaster Mereel, the character is in "no way related [to] or even affiliated with" the canon Jaster Mereel, despite sharing the same name. Why the author chose to use the same name is unknown.