10 Stargate Characters Who Vanished Without A Trace
9. Colonel William Ronson
Colonel William Ronson was the first commander of the Prometheus, Earth's first hyperspace battleship. He quickly got under the skin of Jack O'Neill during the ship's shakedown cruise, though both officers came to understand each other quickly. The very nature of the show has SG-1 effectively saving humanity again and again, while Ronson's continued readiness drills for his crew were designed to ensure against precisely that - having to rely on SG-1 to save their hides the whole time.
O'Neill understood that, though they butted heads again once the Prometheus had to eject its core and land on the Planet Tagrea. Their arrival caused issues for the local population, with Ronson remaining steadfastly against helping them, lest they compromise the ship. O'Neill was able to talk him around.
On a later mission, Ronson is vanished along with the rest of the crew, while studying a nebula at the behest of Samantha Carter. Though he is returned soon after, this would be the last time that he was seen. While he was presumably just reassigned, there is something to be said about the man who lost control of the ship on several occasions and didn't get along with Jack O'Neill.