Autarkist

A sentient being that is completely alone, they can't or won't interact with any other being. One that is completely self sufficient.

Similar meaning to Autarky but more so meant for the only living sentient being of an area/planet.
Pronounced ot-tor-kissed.

It was only after WW3 that the first Autarkist was made.
The autarkist wondered if they were really the last one.