Passive mobs will never attack the player. All passive mobs except squid require land to spawn on. Squid need water to spawn in.
Neutral mobs will not attack the player unless provoked. The act of provoking neutral mobs varies between mobs.
These mobs can be tamed by the player.
Hostile mobs will attack the player when in range. Cave Spiders, Zombies, Creepers, Skeletons, Spiders, and Spider Jockeys require a light level of 7 or less to spawn. All mobs' hostility levels are based on how they are spawned by default. Spiders may become neutral, but they do not spawn neutral.
Utility mobs are created by and serve the player.
Boss mobs have more complicated attack patterns and movements. They also have a large amount of health. Boss mobs only spawn once per world.
Removed mobs have been removed from the game and can only be found in previous versions.