Arland Theirin was a King of Ferelden who reigned in the beginning of the Storm Age.
Background
Prior to his coronation, there was no clear successor and both Arland and Arlessa Sophia Dryden had a strong claim to the crown. According to Dryden's journal, he was chosen instead of her because he was young and thought to be easily manipulated by the arls and teyrns, but she had seen "something in the boy's eyes, that terrified her".
It was not long before he showed he was an immoral, ruthless leader and he imprisoned Sophia for contesting for the throne of Ferelden, however he spared her but forced her to join the Grey Wardens. Eventually, some of the Banns sought Sophia out for help against his tyranny. A letter from Bann Mathuin Wulff can be found in Soldier's Peak where he explains how Arl Ruahn and his entire family had been slaughtered for an idle word, thus ending the Ruahn line, and begging Sophia for her help.
As soon as he learned that Sophia was using the Grey Wardens as an army to oppose him and that there was a rebellion against him, he forbade all tithing to the Wardens. He then outlawed the Grey Wardens and his army was sent to Soldier's Peak where they besieged the Wardens for months. He eventually emerged victorious.
Arland also executed many Couslands including the Teyrn himself, for plotting against him, being allied to Sophia, and to teach the survivors their place.
Little is known of what followed Arland, as a civil war for the throne occurred soon after his death. The war lasted a decade and wiped away most records of his rule.