This colleague's main aim is to invade your personal space, whether they're just 'popping over' for a chat, or draping themselves over your desk to see what you're up to, this person seems like they just want to be next to you ALL of the time.
In this situation it's a good idea to be pro-active rather than reactive. Make your area unwelcoming. Place your bag or briefcase next to you on the floor and fill your normally minimalist bench desk
and any spare chairs with papers, books and anything else you can think of to ensure the Personal Space Invader has nowhere to park themselves.