A hoglin (Via screenshot)
Hoglins spawn in the crimson forests usually in groups of 4. They can spawn on top of most blocks except nether warts and shroomlights and can spawn at any light level. 5% of hoglins spawn as babies. Even though they are hostile mobs, they will spawn in Peaceful difficulty and will be passive to players.
A hoglin in a crimson forest (Via screenshot)
Hoglins will attack players within 32 blocks on sight by flinging them into the air. Baby hoglins will also attack you but they deal less damage and won't fling you around as compared to adults. If you have warped fungus or are near it (within 7 blocks) hoglins will not attack you and will run away instead. If a hoglin is brought to the overworld it will start shivering and after 15 seconds it will turn into a zoglin.
When an adult hoglin is killed it will drop:
Other than killer bunnies, hoglins are the only hostile mob that can be bred. To breed hoglins you will need to feed them crimson fungi. Like with most breedable mobs, they have a 5-second cooldown before they can breed again. Baby hoglins need 20 minutes to grow up, and feeding them reduces the time required to mature by 10%.
Breeding hoglins (Via screenshots)
When a hoglin is spawned or brought to the overworld or the end, it will start shaking and shivering, and transforms into a zoglin after 15 seconds. Leads will disconnect when the transformation occurs, but zoglins can be leashed with the lead as well. 20 seconds after transforming, the zoglins will have a Nausea effect which is mostly a decorative effect as it doesn't affect its behavior.
A zoglin in the overworld (Via screenshot)
If you are in the Nether, you can rely on hoglins as a reliable food source, but be careful as they have the ability to fling you around.
A. No, you cannot tame hoglins.
A. Hoglins are afraid of warped fungus.
A. No, they cannot be protected from zombification in the overworld.