Spanish navigator Bruno de Hezeta first discovered the Columbia River in 1775, but did not attempt to enter it. He thought it might be an estuary for an inland bay or "the mouth of some great river or some passage to another sea."
Instead, the honor of naming the great river fell to Capt. Robert Gray of Boston. In search of ways to expand the fur trade, he navigated the bar in May 1792 and discovered the river he would name for his ship, Columbia Rediva. For another two years, Gray continued to explore the shores north and south of the river's mouth.
Not about to let Americans claim the area, the British quickly dispatched two ships to the Columbia five months later – HMS Discovery, commanded by Capt. George Vancouver, and HMS Chatham, commanded by Lt. William Broughton.
Since Capt. Vancouver was unable to get his larger ship past the bar, Lt. Broughton took the Chatham some 100 miles upstream to Washougal, and claimed the area in the name of England. The lieutenant, being a wise man, named the area near present-day Vancouver after his boss.
To read more about Vancouver, see Fur traders and Hawaiians.