Usurper is the name of the Ealdremen System's second star, the other bearing the name of Topple-King. The only known habitable planet to orbit Usurper is Nethere, and its cultures have historically simply called this stellar body "the sun" in their own native languages. The name Usurper is meant to deliberately contrast Topple-King while also alluding to the way that the discovery of this star and its orbiting bodies "usurped" conventional understandings of Ealdremen space.
As a recently-coined term, the name Usurper is not in use in every culture even within kingsward regions and has not had time to proliferate in the way that Topple-King, an originally Morish term, eventually did through its centuries of use by Ealdremen's most prominent scholars. The name was dubbed by the astronomer Riu Lao-Ji, the first known Ealdremen scientist to charter meaningful amounts of kingsaway space.