Where does “stalker” come from?

stalker (Dutch) comes from English stalker, from Middle English stalkere, from Irish -aire, from Old Irish -aire, from Old French -aire, from Latin -ārius, from Proto-Italic *-āzios — Forms relational adjectives to nouns (and rarely numerals).

stalker (Dutch): stalker (a person who secretly follows someone, sometimes with unlawful intentions)