Head angle, the slacker the more the self-centering (castering) effect
&
Trail, the more trail the more the bike wants to go straight.

Trail is a combination of wheel radius, head angle, and fork rake (or offset).

However it is not really as simple as that because other things like wheelbase and center of weight affect it some but not as much as those do. Also extremes do not seem to work well, so it is a case of balancing the effects of angle and trail within a fairly narrow range. The trade offs are quick steering vs. steadiness. most modern bikes are designed for quick steering, many older (pre early 70's) bikes were designed for steadiness.