INTERLOPER
intruder, interloper, trespasser
(noun) someone who intrudes on the privacy or property of another without permission
Source: WordNet® 3.1
Etymology
Noun
interloper (plural interlopers)
(obsolete) An unlicensed or illegitimate trader.
One who interferes, intrudes or gets involved where not welcome, particularly a self-interested intruder.
Source: Wiktionary
In"ter*lo`per, n. Etym: [Pref. inter- + D. looper a runner, fr.
loopen to run; akin to E. leap. See Leap, and cf. Elope.]
Definition: One who interlopes; one who interlopes; one who unlawfully
intrudes upon a property, a station, or an office; one who interferes
wrongfully or officiously.
The untrained man, . . . the interloper as to the professions. I.
Taylor.
Source: Webster’s Unabridged Dictionary 1913 Edition