interloper

The story

From inter- + loper (“runner, rover”), as in landloper (“vagrant”) (from lope (“to leap, to jump”) (originally dialectal)). Originally spelt enterloper and used in specific sense, “unauthorized trader trespassing on privileges of chartered companies”, later general sense of “self-interested intruder” from 1630s.

First known use, by meaning

• from 1630s One who interferes, intrudes, or gets involved where not welcome; particularly, a self-interested intruder.
• 1590s to ? An unlicensed or illegitimate trader.