This is a reasonable question. Firstly cats see us as providers and surrogate mothers when being cared for or on occasions confusingly as kittens when bringing prey back to their owners’ home.
They may be aggressive towards their owner for specific reasons which don’t undermine that relationship. The overriding factor is that domestic cats have all the characteristics of their wild cat ancestor which includes aggressiveness when instinctively required.
The ‘Raw Cat’ beneath – the wild cat character – is near the surface. They want to do what their wild cat cousins do: hunt, catch, kill, eat, groom, sleep (to quote Jackson Galaxy).
For instance, if a domestic cat is not completely socialised, and was raised as a feral cat when weeks old, he may hiss at his owner if the owner tries to get some food or prey off him. It is just an instinctive reaction of survival.
Poorly socialised domestic cats will be prone to returning to their wild cat instincts and attitudes in a human household. They’ll feel uncomfortable and anxious leading to the occasional hissing and bouts of aggression unless great respect and patience is shown.
Even well domesticated and socialised cats can be genuinely aggressive towards their owner if for example they are exercising transferred aggression. Yesterday my cat had a spat with a fox through the garden cat confinement fence. His tail was fluffed up when I called him in. As soon as he came in he bit my bare leg. That was transferred aggression. He wanted to bite the fox. I am glad he was prevented from doing so.
Domestic cats are barely domesticated. If something happens that spooks them it might make them aggressive. He might direct that aggression at his owner if the owner mishandles him under the circumstances.
If a male domestic cat has not be neutered he is more likely to act on his hormones and be aggressive during mating times. This aggression may be directed at a person.
Often cat aggression is due to overexcited play or being over-handled causing irritation.
These are examples. I am sure visitors can think of more.