He is the captain of the Martell guard and the personal bodyguard of Prince Doran Martell, the ruler of Dorne.
Areo Hotah is originally from Norvos, one of the northern Free Cities. He joined the Martell household at Sunspear along with Prince Doran's wife, a Norvoshi noblewoman. He has been a trusted servant of the Martells for many years, and is renowned for his skill with his longaxe. Hotah's motto is "Serve, Protect, Obey".
Areo Hotah is overlooking the Water Gardens with Doran when Ellaria Sand tries to approach the Prince. Hotah blocks her passage, and tells her that the Prince does not wish to be disturbed. In turn, she threatens him, yet Hotah does not move until Prince Doran tells him to let her pass. She berates Doran for doing nothing about his brother's murder, and tells him that she and Oberyn's daughters want Dorne to take up arms and avenge Oberyn. She also wants to harm Myrcella Baratheon in order to send Cersei Lannister a message. Doran strictly forbids her from harming Myrcella while he rules. Ellaria voices doubts that Doran will remain in power if he continues to do nothing, and then storms off. Hotah lets her pass, yet meaningfully indicates his axe to the Prince, but Doran shakes his head and returns his attention to the Water Gardens.
As Trystane and Myrcella take a walk through the Water Gardens, Areo and Doran watch over them. The prince tells his captain that they need to protect the two, as a betrothal between two Houses who hate each other will only lead to danger for both of them. He asks if Areo remembers how to use his longaxe as it has been a long time since he used it last. Areo assures him that he still remembers how.
Areo leads the Prince's guard to break up the fight between the Sand Snakes and Jaime Lannister and his accomplice, Bronn, when they try to take Myrcella. Obara angrily claims that they fight for Dorne and asks who he fights for. Areo repeats his command that they drop their weapons. Surrounded and outnumbered, the Sand Snakes obey. Areo moves fast and places his longaxe at Jaime's neck, telling Jaime that he would have enjoyed fighting him had Jaime had the use of his right hand. Jaime then drops his sword and the guards take them all into custody. Ellaria Sand is also arrested for her part in the attempted kidnapping.
Areo later escorts Myrcella to visit Jaime in his chambers, saying that Doran sent her to quiet Jaime's concerns about her safety. Areo takes his leave, and Myrcella proceeds to have a tense conversation with Jaime in which she says that her mother doesn't really care about what she wants, that Dorne is her home now, and she still intends to marry Trystane Martell.
On Doran's orders, Areo frees Bronn from custody and takes him before his lord. On Trystane Martell's request, Areo strikes Bronn across the face in retaliation for Bronn striking him earlier, in exchange for Bronn being shown mercy.