The principal habitant of the nether world, if the nether man go to your world the sand and dirt is comming to transform into nether sand, but the nether monsters take more damage from the water.
The legendary nether dragon is the nether king and can destroy all the world in a lot of seconds, this drop a special item whit more resistance called nether dragon scale, and dragon egg to spawn The legendary nether dragon (tamed).
Nether Dragon scales
Whit that item the players can craft dragon armor, dragon blocks and dragon stairs or slabs, more powerful and whit more resistance.
Tamed Nether dragon
This only can be spawned whit a dragon egg, if you right click that whit a saddle you can start to drive and fly whit the dragon ( only owner can make this ).