listen to the pronunciation of interloper
Englisch - Englisch
One who interferes, intrudes or gets involved where not welcome

Microsoft thought Linux as a new interloper, who was stealing away the Desktop market.

An unlicensed or illegitimate trader
One who interlopes; one who unlawfully intrudes upon a property, a station, or an office; one who interferes wrongfully or officiously
disapproval If you describe someone as an interloper, you mean that they have come into a situation or a place where they are not wanted or do not belong. She had no wish to share her father with any outsider and regarded us as interlopers. = intruder. someone who enters a place or group where they should not be (inter- + -loper (perhaps from hleapan or lopen ))
someone who intrudes on the privacy or property of another without permission
{i} one who trespasses on the domain of another without proper license (as in trade); meddler, intruder
A person who, without legal right, runs a business (eg without mandatory licenses), or who wrongfully interferes or intercepts another's business
{n} one who interferes wrongfully
plural of interloper