He sailed the Spanish Main trying to capture (and sometimes succeeding in capturing) merchant ships, but quite a lot of the time he was licenced to do that by the British government. So that makes him technically a privateer.
The British government thought so much of Dampier that he was eventually given command of a Royal Navy ship. Mind you, it was such a wreck of a ship that it sank under him - and then when he finally got home he was court-martialled (for cruelty) - but that doesn't mean he was anything like a pirate. Does it.
Dampier had very many adventures on the seas. He was the first person to sail round the world three times; he made some of the first notes about the plants and animals of what later became known as Australia (and drew some of the first charts of Australia, too); he rescued Alexander Selkirk, who inspired the story of Robinson Crusoe; he was known to Johnathan Swift, who put Dampier into Gulliver's Travels.
In 1697 Dampier wrote a book himself. It was called A New Voyage Round the World, and he publicised it by showing (for profit) the tattooed Prince Jeoly and his mother, both of whom he had purchased on his voyage.
Now tell me: does that sound like a pirate to you?
As well as slaves and stories and science and sensation and spoils, William Dampier brought words back with him from his travels: sub-species, avocado, breadfruit, caress, cashew, chopsticks, petrel, posse, snug and barbecue are all words that he seems to have been the first to write down.
And the words, at least, must have been acquired honestly, too.
Word To Use Today: one of Dampier's. Cashew, for example, comes from the Portuguese cajú , from the Tupi acajú.