Xander was An Immortal (notice the Caps). He was bitten and... kinda turned by Spike? I think his body was found and he was given a funeral before Buffy staked him. Giles called someone to train Xander as an immy.
After that Xander was sorta connected to Spike, like his Childe. Later on he ends up as a Marquis on Voyager. Spike finds him no matter where he goes. That's all I remember; help?