Lupa

Lupa is the immortal she-wolf that raised Romulus and Remus, the twin sons of Mars and founders of Rome.

History
Lupa is the head of the Roman Camp Half-Blood in San Francisco, California, much as Chiron is head of the Greek Camp Half-Blood in Long Island, New York. She presumably has the same pact with the gods as Chiron does, which means that as long as they are needed to train half-bloods, they will remain immortal (though it is possible she is a wolf goddess). Harsher than Chiron, she does not aid or raise weak demigods and runs a harsher, more discipline and more militaristic camp. She lets the mortal parents leave their demigod child(ren) at the Wolf House (a house formerly owned by Jack London, a novelist) at a young age(around 2 years). If they show weakness, she eats the babies. If they show potential, she takes them to the Roman Camp Half-Blood and nurtures them as if they were her own babies (albeit in a harsh "survival of the fittest" way) and trains them in the ways of a Roman soldier. While she is still extremely strict, it is inferred by her appearance and slight memories by Jason that she has a (slightly) calmer, even humorous and caring side, as when Jason realizes his last name is Grace, making him Thalia's younger brother, he imagines/remembers a proud Lupa laughing at him. She can speak both Latin (and even possibly created latin) as well as English it was shown in Lost Hero when Jason was dreaming that she can also speak some sort of "wolf lauguage" as well. She is the leader of all wolves though she has a strong rivalry with Lycaon the first werewolf.

Feeder of the sons of Mars
In Ancient Roman Mythology, it was believed that the city of Ancient (and later modern) Rome was founded by one of the sons of Mars, the Roman counterpart of the Greek war god, Ares, Romulus, after he and his brother became of age of childhood from the care of the immortal she-wolf, Lupa.

The Lost Hero
Lupa contacted Jason in his dreams to warn him about Gaia inadvertently. She also calls Jason their "Saving grace" and smiles as if she just made a joke. Jason, not knowing his last name at the time doesn't see the humor. It isn't until he learns who he is that he understands what Lupa meant. Later, when Lycaon attacks Jason and his friends, he makes a reference to Lupa, saying that soon Lupa would have to think twice before attacking his pack. Interestingly, as leader of the Roman camp, she still knew where Jason was and was able to contact him in a dream, and yet Chiron, the director of the Greek camp, has not made any mention of being able to contact Percy.

Appearance
She is described in wolf form with beautiful chocolate red fur and eyes as silver as mist. She is also described as being very tall, taller than any human.