I have been trying to recall what this book is from almost thirty years, I read it as a teen. I think it was published in the 1980s.
The story takes place in a distant space faring future, where everyone is catalogued and designated by a galactic A.I. super-computer (space S.S. of a sort). The galactic government is tyrannical, and a small time private detective is recruited by a rebel faction to be the perfect weapon/spy to bring down the computer and government.
In this novel's universe, some people are born with mutations and abilities. The main character is a mutant whose power is that he can not be remembered for more than a day by anyone that has encountered him. Consequently, he is the perfect foil to this A.I. computer, as no one could ever remember him as to record his birth, thus he's off the grid and technically does not exist.
I recall that he may also have either a mutation that has caused him to have one hand that is larger than the other, or it's a transplanted hand from person a dark skinned Sub- Saharan descent. The main character is Caucasian (per the cover).