Logan Series by William F. Nolan, George Clayton Johnson, Charles Moll

It's the 23rd Century and at age 21... your life is over! Logan-6 has been trained to kill; born and bred from conception to be the best of the best. But his time is short and before his life ends he's got one final mission: Find and destroy Sanctuary, a fabled haven for those that chose to defy the system. But when Logan meets and falls in love with Jessica, he begins to question the very system he swore to protect and soon they're both running for their lives... moreIt's the 23rd Century and at age 21... your life is over! Logan-6 has been trained to kill; born and bred from conception to be the best of the best. But his time is short and before his life ends he's got one final mission: Find and destroy Sanctuary, a fabled haven for those that chose to defy the system. But when Logan meets and falls in love with Jessica, he begins to question the very system he swore to protect and soon they're both running for their lives. When Last Day comes, will you lie down and die... or run! less

Logan's world. . . With the computer system destroyed, Earth has reverted to savagery. Scattered tribes now rule a charred world. Scavengers, who prowl the broken cities. Surviving corps of the elite killers, led by a psychotic ex-Sandman. Sadistic bands of gypsy riders who kill and plunder. When tragedy strikes, his loved ones, Logan sets out on a death-haunted vengeance trail across a ravaged world that leads to a startling confrontation and ultimate destruction.

Logan is running again, with the fate of the world in his hands. Earth is free and at peace at last. But not the Earth on which Logan stands. For him a nightmare has just begun...In the 23rd century on Parallel Earth your 21st Birthday is your Lastday. Parallel Earth is a dazzling paradise of pleasure and infinite joy. Here, in a terrifying computerized society controlled by ruthless police assassins, is the world that Logan once destroyed. Now his fate is to live that horror once again.

William F. Nolan and George Clayton Johnson. Logan: A Trilogy. Baltimore: Maclay and Associates, 1986.