The Dark Beyond the Stars by Frank M. Robinson
Sparrow is a crew member on the Astron , a multigenerational ship sent from earth on an unavailing, 2000-year search for other life-bearing worlds. On the last planet, Seti IV, Sparrow fell off a cliff and nearly died, losing his memory in the process. While recovering in sick bay and also while back on the job, he is beset by more accidents. Eventually he decides that someone is trying to kill him. Trying to find out who and why, Sparrow is plunged into an ever-deepening mystery; nobody will discuss his past with him, the computer has restricted his data, and the little he does discover about his history leads only to further secrets.
Excellent dialogue, suspenseful situations, and some of the most memorable characters I have ever come across. Probably my second favorite book after Dune if that says anything. I actually want to reread it just thinking about it.