Arys Oakheart

Arys Oakheart is a recurring background character in the first, second and fifth seasons. He is played by an unidentified extra and debuts in "You Win or You Die". Ser Arys is a knight and a member of the Kingsguard and defends King Joffrey Baratheon as he defended King Robert Baratheon before him. He is sent with Princess Myrcella Baratheon to Dorne.

Season 1
Ser Arys was among the guards that attacked Eddard Stark when he tried to de-throne King Joffrey. He was also present when Ser Barristan Selmy was dismissed from the brotherhood

Season 2
Ser Arys accompanies Princess Myrcella Baratheon as her sworn shield for her journey to Dorne.

Season 5
Ser Arys returns to King's Landing after Myrcella's arrival in Dorne and escorts King Tommen in his attempt to enter the Great Sept of Baelor to speak to the High Sparrow about the arrest of Ser Loras Tyrell.

In the books
In the A Song of Ice and Fire novels, Arys Oakheart is a member of Robert Baratheon's Kingsguard, appointed after his predecessor - whose name hasn't been mentioned - perished during the Greyjoy Rebellion. He's a member of House Oakheart, a noble house from the Reach.

He is regarded as one of the kinder Knights of the Kingsguard under King Joffrey, objecting at first to Joffrey's orders to beat Sansa Stark, then only hitting her as lightly as he dares. He is also of a much more pleasant demeanor, often engaging in pleasant conversation with the Stark girl.

Arys remains in Dorne as Myrcella's sworn shield. During this time, Arianne Martell, Prince Doran's daughter and heiress, seduces him. She persuades him to take part in her plan to crown Myrcella to incite war with the Iron Throne in retaliation for the death of Oberyn Martell. The plan is foiled, and Myrcella is gravely injured and nearly killed by one of their escorts, Ser Gerold "Darkstar" Dayne.