Tempest (storm spirit)

Tempest is a ventus that was found in The Lost Hero.

The Lost Hero
In the battle against the giant Porphyrion at the Wolf House, Jason Grace uses his power to control wind to tame Tempest to help him in the fight. Tempest manages to survive when Hera unleashes her true form after she is released from her cage by Leo Valdez and Piper McLean. However, Tempest "scatters" off and it is currently unknown where he is, but Hera tells Jason he will see Tempest again.

The Mark of Athena
Tempest is seen on the front cover of the book being ridden by Jason against Percy Jackson and Blackjack. He is called by Jason to ride towards Bacchus during their trip to Kansas. After being possessed, Jason, on Tempest, fights Percy, on Blackjack. Jason states that Tempest only comes sometimes when he calls for him.

Appearence
Tempest takes the shape of a horse like some other ventus, instead of taking a humanoid shape.