[net.sf-lovers] I want to find a book

dbell@nsc.UUCP (David I. Bell) (11/24/83)

Several years ago I read a trilogy, and I want to know what it was.

In the first story, the main character (say "Joe") crash landed on an
uninhabited planet, and while there found an invisible creature which took
residence in his brain.  This creature was a "mental symbiote", and could
mentally communicate with Joe, to give him advice and such.  But it (usually)
left Joe able to control his own body and make his own decisions.  Joe resented
the creature's presence, and wanted it to go away, but it was unable to leave
until Joe died, at which time it would find another body to inhabit.

Joe eventually got rescued, and as payment to the rescuer, had to perform
various tasks for many years.  Each of the three books concerns one of his
tasks.  (This setup is a lot like the "Stainless Steel Rat" stories).
Along the way the creature becomes more and more important to Joe, and
after a while Joe doesn't resent it, and instead depends on it to help him.

In one of the stories Joe had to go to a planet where everyone lived
in tunnels.  In the final story, Joe had to fight something in a strange
nebula connected to some alternate universe, and the creature died, leaving
Joe all alone and unhappy.

That is all I remember about the trilogy.  Can anyone tell me what the
titles are, or who wrote them?  Thanks!!