Relius Clover is Carl Clover and Ada Clover's father, and Ignis Clover's husband. He is a colonel in the Engineering Department for the Novus Orbis Librarium, and works alongside Hazama as one of the main antagonists of the series.
Relius is a genius alchemist known as the "Puppeteer". At some point before the start of BlazBlue: Calamity Trigger, he disappeared without a trace.
(Source: BlazBlue.wikia)