One who wrongfully or illegally seizes and holds the place of another.

synonym: supplanter.

Roget 925: undueness etc. adj.; malum prohibitum [Lat.]; impropriety; illegality etc. 964.    falseness etc. adj.; emptiness of title, invalidity of title; illegitimacy.    loss of right, disfranchisement, forfeiture.    usurpation, tort, violation, breach, encroachment, presumption, assumption, seizure; stretch, exaction, imposition, lion's share.    usurper, pretender.    ... show more

Dutch: usurpator, veroveraar
Polish: samozwaniec, uzurpator