Doppelpets are pint-sized clones of SSW players. If an SSW player submits their DNA for cloning at the Doppelpet Manufactory on Laxloo, then other players can purchase doppelpet clones of that player. SSW players who have submitted their DNA receive a royalty payment (in Starbux) each time anyone else purchases a doppelpet clone of them.
Doppelpets are very handy to have around. When you have one equipped, it will help defend you, as well as happily perform various other monotonous tasks that you assign to it. Plus they're cute and cuddly!