Dave Miller x Jack Kennedy — reading through their nicknames

Again, from the wiki:

DAVE MILLER:

Dave is an outgoing and rather unhinged man, showing no guilt for the crimes he committed. While he can be outwardly friendly to others, he's not afraid to kill them at a moment's notice. This is due to Henry tampering with his brain, messing his mind up to the point where he genuinely cannot feel empathy for the things he has done.

Dave seems to have an obsession with Jack (and also with the nickname "Old Sport") judging by how he tries to befriend and putting him in his scheme, he even has a file on his computer's profile filled entirely with the word "Old Sport." The reason behind this attraction is unclear; Dave clearly doesn't need help for his plans as he does it by himself if the player declines the offer. Declining his offer can turn him into Jack's worst enemy, showing how inconsistent their relationship can be.

JACK KENNEDY:

The Freddit events the player can choose to trigger seems to show that Jack can be a little immature or even childish at times. This could be a joke, but Jack does this completely on his own, without any player input. He even acts this way in some events, such as; doing a flip to prove his dominance, wanting to dive into the Ball-pit, and refusing to get off the slide. He also has a few phrases that make him sound childish, but these can be picked by the player, so they might not be some of his own actions.

In DSaF 2's Pure Evil ending, Jack snaps and enters a sadistic state that scares Dave and Peter, causing the latter to call you a soulless monster that thrives on death. This also makes Fredbear say that you make both Dave and Henry look like jokes. Fredbear also states that they killed kids, and Henry did something to Dee. After Jack beats Fredbear, Dave says that he thinks Jack "killed the fuckin' concept of childhood."

Depending on the ending of DSaF 3, Jack has three different reasons for reviving Freddy Fazbender's. In the Good Ending, Jack created the new pizzeria to lure DaveTrap and the remaining spirits, to get rid of them for good. In the Neutral Ending, Jack instead uses his ownership to get back at his time working at Freddy's. In the Evil Route Jack uses the pizzeria as a front to continue murdering children.