THE HOST:

... Dr. Lester is well aware of the portal and has been using it to live on for year after year, changing from one dying body to a younger one each time. When the body is "ripe," the portal moves to its next host. Anyone who manages to enter the portal at the right time when the body becomes "ripe" gets to live on in the body. At the present time, the portal is connected to the body of Malkovich, which is getting "ripe" soon. Dr. Lester reveals to Lotte his plan to use Malkovich as a host for himself and several of his friends.

A living body (John Malkowitch) is used as a host that can be entered by others through a portal. Entering the host at the right time allows others to live on year after year through the body. When the occupied host is getting “ripe” the body needs to be changed to a younger one.

The host is not aware of his occupation. Not that his body is used as a mask. He is dealing with life as usual. Embedded into his environment. Fully under control of himself.