Trian of House Aeducan is a commissioned Commander in Orzammar's army and the elder brother of the Dwarf Noble and Bhelen Aeducan and subsequently is the logical choice for an heir, but many believe that he will be a terrible king. Furthermore, he doesn't have enough support in the Assembly to be easily elected as a king. Only the Dwarf Noble can meet Trian, but all will learn of him regardless of origin story as Trian is mentioned while the Warden's party is in Orzammar.
Dwarf Noble Origin
Trian is first encountered in the Diamond Quarter along with his youngest sibling and second, Bhelen, during the quest The Nobles' Feast. He will be abrasive and demand that the Dwarf Noble go to the feast in their honor.
After the feast King Endrin will ask the Dwarf Noble to locate Trian. If you fought in the Provings or watched them and conversed with the Proving Trainer, Trian will be located in his room in the Royal Palace. Otherwise he will be located in the Proving Grounds. He will mention to the Dwarf Noble that it is a meager achievement to be named Commander of Orzammar. When he leaves, Bhelen will reveal that Trian is conspiring to kill the Dwarf Noble as the Dwarf Noble is more personable and well-regarded than Trian and may therefore be chosen as ruler in his place. Here you have the option to dismiss Bhelen's warning or agree that Trian is a threat. If you ask for Gorim Saelac's opinion as the Dwarf Noble's second he will agree that killing Trian is the best option as Trian would make a poor ruler and his lack of support in the Assembly will cause chaos when King Endrin dies and a successor must be named.
The next day the Dwarf Noble is sent into the Deep Roads to recover the ancient Aeducan Shield from the lost Aeducan Thaig along with Gorim, Frandlin Ivo and the Scout. However, once the player reaches the entrance to the area where the shield is located, it is clear that someone is already there and used an Aeducan Signet Ring in order to enter. The intruders are dwarven mercenaries hired to kill the Dwarf Noble and retrieve the shield. If the Dwarf Noble asks how they got inside, their leader, confident that the Dwarf Noble will die soon, will admit that one of Trian's men gave him the Aeducan Signet Ring, implying that Trian may indeed have plotted against his sibling (the persuasion check is always successful). After the ensuing fight the Aeducan Signet Ring is found on the Mercenary Captain's body.
After the Dwarf Noble deals with the mercenaries and recovers the family shield the party comes across Trian Aeducan and his guards. Here, if the Dwarf Noble rejected Bhelen's warning, Trian, along with his guards, will be dead. However, if the Dwarf Noble agreed to kill him, then Trian will accuse the Dwarf Noble of plotting against him. The Dwarf Noble can ask Trian where his signet ring is, provided that they looted the corpse of the Mercenary leader, and he'll suspiciously say that he didn't wear it today for fear that he may lose it. Then he will demand the Dwarf Noble and their party surrender and be judged in front of the Assembly for plotting his assassination. The Dwarf Noble can accept or refuse to surrender. Refusing will instantly initiate a fight while accepting surrender will make the Scout attack Trian and force the fight to begin.
Whether Trian is dead when the Dwarf Noble arrives or is slain by the Dwarf Noble, King Endrin, Bhelen, Lord Harrowmont, and guards will arrive to discover the grisly scene. Bhelen will accuse the Dwarf Noble of murder whether the Dwarf Noble killed Trian or not. The Scout and, with some reservation, Frandlin Ivo will corroborate Bhelen's claim. The Dwarf Noble is accused of murder and taken to a prison in Orzammar to await their trial by the Assembly.
After the OriginOf Noble Birth quest upon return to Orzammar, a male Dwarf Noble who didn't kill Trian in the origin story may choose to name his child after him. Furthermore, if a Warden of any origin chooses to support Bhelen's bid for the throne and elects him king during A Paragon of Her Kind, Bhelen will reward them with Trian's Maul. Wardens of Dwarf Commoner Origin must have completed at least A Prince's Favor: The Second Task in order to receive the maul.