Reyna Avila Ramírez-Arellano is a Roman demigod, the daughter of Bellona, and the younger sister of the current Queen of the Amazons, Hylla, and she is the current Praetor of Camp Jupiter.

Percy describes Reyna in The Son of Neptune as being about sixteen, with piercing black eyes, glossy black hair worn in a single braid, and brown skin. She is often described as having a regal and gorgeously beautiful appearance of Puerto Rican descent and described as having a gaze as if she could take on any challenge. Percy noticed that the worry lines around her eyes made her look older than she probably was, he also describes her as having the 'poise of a sword fighter', relaxed yet vigilant as if she was ready to spring into action at any moment. Like all the demigods in Camp Jupiter, she has SPQR branded on her forearm with four bar lines and a crossed sword and torch, the symbol of her mother Bellona. Being a praetor, Reyna wears a regal purple toga decorated with gold medals over her own Imperial Gold armor, which she wears regularly. In The Blood of Olympus, when Athena gifts her with a portion of her own Aegis, Reyna's purple cloak glitters "as if woven through with filaments of Imperial Gold."

In The Tyrant's Tomb, Apollo says that Reyna is beautiful and imposing and has eyes as piercing as an eagle's. She wears a ponytail swept over her shoulder like a horsewhip. She is even so beautiful that Apollo stops dead in his tracks and is shocked at how beautiful she is. Once she becomes a Hunter of Artemis, she gains the natural silver aura and eternal youth. She is also described as a tall, intimidating, and authoritative young woman with a powerful aura. She often wears her Aegis cloak in a sweater wrap that it can transform into and wears armor as normally as someone wearing t-shirt and shorts.

Reyna is a very strong-willed person. She is very strict with the members of the Twelfth Legion and doesn't like to be questioned. However, the reason she is so strict is because she is determined to protect her family after what happened on C.C.'s Spa and Resort. Because of her past, she does her best to be stoic, doesn't show any signs of weakness around others, and keeps up her mature public image to keep up the moral of the camp. She feels that if she ever appears nervous or scared, her emotions will cause the camp to worry as well. Hence, even though she was very much changed by the Giant War at the end of The Blood of Olympus, her exterior doesn't show it, according to Piper McLean.