usurper vs offender

usurper and offender both are nouns.

Word	Noun	Adjective	Verb	Adverb
usurper	Yes	No	No	No
offender	Yes	No	No	No

As nouns, offender is a hypernym of usurper; that is, offender is a word with a broader meaning than usurper:

usurper: one who wrongfully or illegally seizes and holds the place of another
offender: a person who transgresses moral or civil law

Other hypernyms of usurper include wrongdoer.

usurper (noun)	offender (noun)
one who wrongfully or illegally seizes and holds the place of another	a person who transgresses moral or civil law