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Rogash was a troll that joined the Witch-king of Angmar in the conquest of Arnor, believing in promises of unification between the warring Snow Trolls and Hill-trolls. He was known as the "Troll of the North" by friends and foes alike. He had the built and strength of an average troll but his skill with swords was equal to a trained swordsman. He is a playable hero for Angmar in The Lord of the Rings: The Battle for Middle-earth II: The Rise of the Witch-king. He was slain during the final assault on Angmar.
Rogash is not in any canonical works of Tolkien.
Rise of Angmar
When the Witch-king of Angmar arrived, Rogash was fighting a group of Black Númenórean infantry. The Witch-king and Morgomir helped him to kill the Black Númenóreans. Rogash explained to the Witch King that he wanted to unite the Snow Trolls, Hill Trolls and Dire wolves to steal gold and meat from the men of Arnor. The Witch-king told Rogash that if he wanted to unite all trolls, he would have to serve him. They advanced to the Hill of Snow Trolls where they found a group of Trolls fighting against each other, Rogash stopped the battle and the Witch King asked them to join him against the Black Númenóreans. They agreed to join and killed the all the Black Númenóreans that lived close to their hill. After moving north they found some trolls working as slaves and so freed them and built three fortresses to hold against the Black Númenórean's. After going south Rogash found a group of Cave Trolls and united them to his casue. Since the Black Númenóreans were launching a counterattack, the Witch King and Rogash fled to their southern fortress and defeated the Black Númenóreans when they arrived.
Fall of Amon Sûl
The new king Arveleg had finally defeated Angmar after so many attacks. That he had foreseen with the Palantír of Amon Sûl. The Witch King attacked Amon Sûl with all his forces and had sent a diversion attack to Rivendell and Cardolan. Rogash easily breached their shield walls by jumping over the soldiers. Reinforcements arrived to help the Dunedain. However some Mountain Giants were sent to reinforce the Witch-king. All the Maiar that were allowed Amon Sûl magic powers were destroyed and Morgomir destroyed the tower with his powers. Arveleg fled from the fortress with the Palantír. Morgomir had gone in and persuaded Arveleg. It is unknown if any Dunedian survived or escaped.
Fall of Cardolan
The Witch-king attacked the Barrow Downs knowing that Cardolan would foolishly attack his forces. First he sends Hwaldar, who defeated the initial attacks then Rogash and his Troll Army arrived to destroy the vanguard of Cardolan. Even if the vanguard was made of elite soldiers Rogash and his Trolls where too strong for them. At last the Prince arrived to the Barrow Downs at the same time that the Witch-king with the main army arrived. The Royal Guard of Cardolan was too strong and many Trolls died, but Rogash slew a good number of them. The Witch-king killed the prince in a single duel, and Cardolan was defeated, leaving only Fornost, in the region Arthedain, as the last fortress in Arnor.
Siege of Carn Dûm
The attack on Rivendell united all the Elven realms against Angmar. The Elves of Lindon, Rivendell and Lorien lead by Glorfindel and Elrond march against Carn Dûm. Rogash and Morgomir waited for the signal of the Witch King to arrive with reinforcements. The Witch-king light the signal and Morgomir and Rogash began moving but they arrived too late the citadel was besieged by the Elves but there was still time to save Angmar while Rogash and his army attacked from the back the Elven army the gates opened and the forces of Carn Dûm attacked from the front. Rogash's arrival saved Angmar from total destruction.
End of Arnor
After the Great Plague had weakened Arnor, the Witch-king decides to attack Fornost and have absolute victory over Arnor. All his armies were there to ruin the city. After the main gate of Fornost was destroyed the Shade of the Wolf was summoned. Hobbits of the Shire and of Bree arrived to help Arnor. Rogash with some Trolls and Karsh killed them all. The Troll army came separated from the main army and destroyed the Northwestern parts of the city. They enter the citadel by its western gate where they met with the main army. They took down the monuments of Gondor, which gave them victory.
When Elrond, Glorfindel and Eärnur finally attacked Angmar, Rogash and an army of Trolls waited for them in the Hills of the Snow Trolls. When the army arrived and Earnur challenged Rogash, many Elves and Men fell under the mighty sword of Rogash until Earnur fought against him and killed him. All of his Trolls died and the Witch-king was defeated. That was then the end of the Reign of Angmar, and Carn-dûm was destroyed.