What sort of man was Robert Neville's father in I Am Legend?

In the book, Robert Neville's father was named Fritz. When Fritz was alive, he insisted that his logical temperament would never permit him to accept the existence of vampires. A fan of the scientific method, Fritz needed substantive proof before he could ever admit the possibility of such an incredible hypothesis. Robert states that his father died "denying the vampire violently to the last." Fritz's unyielding position reinforces Robert's claim that "THE STRENGTH OF THE vampire is that no one will believe in him."

Much of what we know about Fritz is told through Robert's perspective. For his part, Robert actually resents the fact that he takes after his father. He feels that, like his father, he is sometimes too obsessed with orderliness and too preoccupied with facts and logical arguments. He later comes to appreciate the trait of orderliness that he has inherited from his father, though.

Grudgingly, almost amused, he soon had a place for everything. Glass slips, cover glasses, pipettes, cells, forceps, Petri dishes, needles, chemicals—all were placed in systematic locations. He found, to his surprise, that he actually gleaned pleasure from practicing orderliness. I guess I got old Fritz’s blood in me, after all, he thought once in amusement.

As mentioned, Fritz believed in the logical approach. Later, Robert complains that he has this same trait himself. He suspects that Ruth is infected with the vampire bacillus, although she denies it. Robert needs to make sure (for the sake of his own sanity). He knows that he won't rest until he tests her blood:

She was going to let him check her blood. What else could she do? It’s me, he thought. I’ve been by myself too long. I won’t believe anything unless I see it in a microscope. Heredity triumphs again. I’m my father’s son, damn his moldering bones.

Robert's suspicions are borne out of the similar nature he shares with his father: the need to be absolutely sure before faith is granted. Through Robert, we come to see that Fritz was a methodical, efficient, and logical man.