I know. I know. Infographics have to work very much harder to be worth your time and attention these days. I think this one, from Shirts.com does. It uses visuals to help you track when various X-Men first appeared, when they stopped being mentioned (often because they died) and when they appeared again.
Professor X, I discovered, first died in 1968. Spoilers; later on we discover the dead mutant was actually the Changeling.
In the blog post announcing the X-Men, Shirt.com asks if the names “Maggott” or “Slipstream” ring a bell. Phew. They do! I’m not a total X-Men noob after all.