Character Analysis
We don't know too much about Oll except that way back when Katsa's Grace was first revealed, he's the only one who "wondered, as it had occurred to no one else to wonder, whether Katsa hadn't been just as shocked by her cousin's death as everyone else" (1.40), which is a fair bit of insight. Katsa was eight at the time, and Oll was already "King Randa's graying captain and […] spymaster" (1.40), so we know he's significantly older than she is.
In some ways, Oll is a kindly father figure to Katsa. It was he, after all, that organized her early training, and he always accompanies her on missions. Also, despite being Randa's spymaster, it would appear—through his work with the Council and his willingness to keep things like the "high doorway in a defunct section of the castle wall […] from Randa's notice" (2.16)—that it is actually Katsa to whom he is most loyal.
His sense of humor—such as when he tells Giddon, "Let's eat our bread in the saddle. Otherwise our lady will leave without us" (3.16), or when he chuckles over Katsa and Po's first fight, saying "Oh, how I would love to have seen it" (9.65)—furthers his image as a kindly father figure. And when he makes comments to Katsa such as, "[Giddon] gets a little mopey whenever your name is mentioned, Lady. I won't pretend I don't know why" (39.32), we are reminded of no one so much as Alfred, the kindly butler, caretaker, and lifelong friend of a man named Bruce Wayne.