Since nearly all trolls are named after the thing they first ate, Dad has acquired his name from eating (or trying to eat) his father. This is further confirmed by Dad himself, as Dad replies "Troll named after first thing try to eat!" when a player asks about his name before battling him. He challenges players, either doing Troll Stronghold or not, to fight him in the troll arena so players can pass him and have access to the northern side of Troll Country including the God Wars Dungeon. He will stop the player from attacking just before he dies to ask you to spare his life. It is recommended that you spare his life, because if you choose to kill him after he has surrendered, he will drop big bones and you may continue, but all the troll spectators in the arena will become aggressive towards you and will try to kill you, so if you kill him, be ready to run to the northern gate. If you just let him live, he will allow you to pass through the gate anyway, and the troll spectators won't become aggressive.
He is known to have a son, who ate him and thus too his name.
Dad is larger and stronger than normal Trolls, so much he actually wields a large, hollow tree trunk in battle. He is very powerful and can hit into the high 200's, and his hits can be slow and fast at times. When he hits there is a chance that he may do a giant swing that sends player flying through the air, momentarily stunning them. Protect from Melee is recommended when fighting him. Despite his strength, Dad is notable for being one of two non-aggressive trolls which can be fought, the other is the troll spectator. This is probably because he seems to be a troll with a sense of honour. You must stay near a wall while fighting him or else he will stun and throw you to the wall
Once Dad is killed players will not be able to kill him again outside of the Dominion Tower. Since the troll update, it is possible to fight Dad again and kill him multiple times. This might be a bug. Dad WILL count towards a troll slayer assignment, but fighting him is not advised. Besides hitting hard, you barely get any combat experience and just 3 Slayer experience.