Well tenant is the antonym of landlord.
From Oxford English Dictionary (OED):
Originally, a lord or owner of land; in recorded use applied only spec. to the person who lets land to a tenant.
One who holds a piece of land, a house, etc., by lease for a term of years or a set time. (The ordinary current sense. Correlative to landlord.)
Lodger would also strangely be the closest antonym for lodger.
One who resides as an inmate in another person's house, paying a certain sum periodically for the accommodation.
One who lodges a person; a host. Obs.
Renter may also apply, depending on how the word is used:
A person who collects rents (esp. those belonging to a corporate body), taxes, or tribute.
A man who lodges and entertains for payment; a man who keeps a public place of lodging or entertainment; the landlord of an inn.