Interloper

n. one who trespasses on the domain of another without proper license (as in trade); meddler, intruder

The word interloper can refer to:Interloper (comics), in Marvel ComicsAn interloper in e-commerce, someone that interferes with the session during which data is interchangedAn interloper in finance, a company that swoops in with a higher bid for an acquisition once a bid has already been made on a companyInterloper, a level in Half-Life and the members of a website concerned with modding of Half Life, Half Life 2 and other games based on the Source engineInterloper, a member of the Twili race banished to the Twilight Realm in The Legend of Zelda: Twilight PrincessInterloper (song) a song by  Slipknot
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Noun
1. someone who intrudes on the privacy or property of another without permission
(synonym) intruder, trespasser
(hypernym) entrant
(hyponym) boarder
(derivation) interlope

(n.)
One who interlopes; one who interlopes; one who unlawfully intrudes upon a property, a station, or an office; one who interferes wrongfully or officiously.
  

A person who, without legal right, runs a business (eg. without mandatory licenses), or who wrongfully interferes or intercepts another's business. - (read more on Interloper)