Similar in that they may be of the same solar "family". One have theorized an extrasolar origin for Pluto because of it's unusual orbit. Maybe it is a Kuiper Belt object that got pulled or perturbed into a closer orbit, or maybe something from "outside" the solar system that was wandering by and got captured.
Lots of interesting ideas out there about the Pluto-Charon pair that differ from the models proposed for planetary formation of the closer-in guys.