Harrold Westerling
Ser Harrold Westerling was a knight of House Westerling who rose to Lord Commander of the Kingsguard, the order of seven white cloaks sworn to protect the king. He served under Viserys I Targaryen, though almost nothing survives about his years leading the order.
His exact place in the Westerling family tree is unclear too: he is linked to Lord Roland Westerling, head of the house, and to Roland's daughter Johanna, without the sources saying how they were related.
Chapter 1
A Westerling in command of the Kingsguard
Books and show
No one has managed to pin down when Harrold took command of the Kingsguard. The earliest possible date would be 105 AC, when Ser Ryam Redwyne, his most likely predecessor, died — though there is no certainty he succeeded him right away.
Through those years he served King Viserys I Targaryen, and no deed or episode of his time leading the white cloaks has come down to us.
What tied him to the rest of his house is also unclear. Lord Roland Westerling led House Westerling during the Dance of the Dragons, and his daughter Johanna was married to Jason Lannister; whether Harrold was closely related to them, the sources do not say.
Chapter 2
Criston Cole's replacement
112 AC
Ser Harrold died in 112 AC.
His death left the command of the Kingsguard vacant, and it was Ser Criston Cole who took it up, leading the same order Harrold had headed until then.
Gallery

Harrold Westerling, image 2Rhaenyra Harrold Tournament Promo.jpg · gameofthrones.fandom.com · this wiki publishes under CC-BY-SA 
Harrold Westerling, image 3OT Harrold, Viserys and Daemon.png · gameofthrones.fandom.com · this wiki publishes under CC-BY-SA 
Harrold Westerling, image 4OT Young Rhaenyra and Harrold.png · gameofthrones.fandom.com · this wiki publishes under CC-BY-SA