Short for Worthy Oriental Gentleman. The Brits tried to stop more disparaging names and ended up with Wog.
"Back in the days of the British Empire, the Brits had a rude word for the natives of the countries they ruled: wogs. It was said to be a derisive abbreviation of the phrase worthy Oriental gentlemen. Later an anonymous wag observed, 'Wogs start at Calais' that is, right across the English Channel. Even the French were wogs!"