Paladins are the ultimate protectors of good. Composed of pure elemental magic, Paladins can be summoned when their Bondeds are in great need. A Paladin is required for a Mage to bond with, and essential for a Mage to get to Level Two status, opening up greater degrees of magical abilities. There are only four known Paladins in the series.
Phelonius, or Phel, was most-likely the first. He is Ozzie's Paladin, though it is unknown when they bonded, either in Circles in the Stream or when Ozzie first received his ferret stone. The two knew each other long before the events of Circles in the Stream, and seem to have a brotherly relationship. However, in the end, they do care very much for each other.
Stormbringer is the Paladin of Adriane. She bonded with Adriane before the start of the series, but did not become a paladin until after her death in Trial by Fire. Their relationship is extremely close, and each would give up their lives for the other. They always want the other to be happy, even if it meant the other had to leave.
Starfire is Kara's Paladin, and is made purely out of the fire element. He bonded with her in All's Fairy in Love and War. They have a healthy relationship, as Kara shares her memories with the firehorse, since he has none of his own and was unable to recognize any emotion other than anger. This changed when he and Kara shared their memories. They aren't shown together much, but Starfire always comes when Kara needs him most.
Indigo is the fourth and last Paladin. He bonded with Emily and became her paladin in Heart of Avalon and is shown to be quite protective of her, using his shapeshifting abilities to scare off anyone who dares to harm her. They are accepting of each other, shown towards the end of Heart of Avalon when he is stuck in the form of a gray blob, but Emily still loves him dearly.