- Eddard Stark: "I looked for you on the Trident."
- Arthur Dayne: "We weren't there."
- Gerold Hightower: "Your friend, the Usurper, would lie beneath the ground if we had been."
- — Gerold Hightower to Eddard Stark[src]
Ser Gerold Hightower's entry in The Book of Brothers mentions several events of his life. Among them are his injury defending the honor and property of Princess Elia Martell; granting temporary command of the Kingsguard to his sworn brother Ser Arthur Dayne, the Sword of the Morning. The Book also mentions that he was sent to locate Prince Rhaegar Targaryen in the wake of Robert's Rebellion, and his death along with Ser Arthur and Ser Oswell Whent near the Red Mountains of Dorne fighting a small force led by Eddard Stark after refusing to bend the knee to the new king, Robert Baratheon.
In Bran Stark's vision of the events at the Tower of Joy, Ser Gerold Hightower fights alongside his fellow Kingsguard, Ser Arthur Dayne, against Eddard Stark, Howland Reed and four other Northmen. Before they commence battle, Ser Gerold declares that Robert Baratheon, who he calls "the Usurper", would have perished instead of Prince Rhaegar at the Trident if he and Arthur had been there. He does not say the same about Ned, even though he fought on the opposing side. Though Ser Gerold manages to kill one of the Northmen, he is slain shortly thereafter by Ned.
Down in King's Landing, the Hand of the King Kevan Lannister objects to his nephew Jaime attending a small council meeting. Jaime counters by stating he has a position there, given he is the Lord Commander of the Kingsguard. Cersei then asks Pycelle to vouch for his presence there, and the Grand Maester brings up the precedent of Gerold being on the Council during Aerys II's reign.
In the books
In the A Song of Ice and Fire novels, Ser Gerold Hightower was known as "the White Bull" for his immense strength. He was Lord Commander of the Kingsguard during the brief reign of King Jaehaerys II and then under King Aerys II.
Gerold Hightower was blindly loyal to the Mad King, no matter how cruel and bloodthirsty Aerys was. He was present when Aerys executed Rickard Stark and his son. He noticed that Jaime Lannister was uncomfortable and inwardly disapproving (from Jaime's thoughts in a POV chapter) of this unjust atrocity and told him, "You swore a vow to guard the king, not to judge him."
During Robert's Rebellion, Prince Rhaegar left Ser Gerold and his fellow Kingsguard Ser Oswell Whent and Ser Arthur Dayne to guard Lyanna Stark at the Tower of Joy near the Red Mountains of Dorne. After the Battle of the Trident, Eddard Stark and six companions arrived to rescue Lyanna and were confronted by the Kingsguard. Despite it being apparent that the Targaryens had lost the war, Ser Gerold refused to surrender, insisting that "the Kingsguard does not flee." In the fight that followed, all three Kingsguard were slain, along with five of Stark's friends. Only Stark himself and Howland Reed survived. It is unclear exactly who killed Ser Gerold. Lord Stark later had the tower demolished and used the stone to make eight cairns, in honor of the eight who died there. It is possible that the TV Show merged the characters of both Ser Gerold and Ser Oswell, as Ser Gerold was supposed to have been much older than the other two knights. Yet, in the show he appears of age with Ser Arthur.
Ser Loras Tyrell, one of the more famous knights from the generation after Robert's Rebellion, is actually related to Gerold Hightower: Ser Gerold was the uncle of Loras's grandfather Lord Leyton Hightower. Mace Tyrell's wife is Alerie Hightower, daughter of Leyton Hightower (Alerie doesn't appear on-screen in the TV series due to time constraints).