Legal Question in Real Estate Law in California

Technicially he is a trespasser but I doubt the local sheriff will physically evict him [call and see what they will do]. You probably will have to sue; you need to go to a local real property/landlord/tenant attorney and find out what can be done. You also need to look at what ever documents were ilnvolved in your gettling ownership to see if the transfer requires the other party to turn the place over to you wlith the old owner out of the house. If it was a foreclosure, whlich I assume it was, and you were unaware the owner was still there, yo wuld be on firmer grounds to insist the lender get rid of the former owner. As a practical matter, it would be much cheaper to pay him a bribe to leave without damaging the place.