Protectors are a form of summons in the world of Final Fantasy XVI. Protectors are the offspring of relationships between Gods and Humans, making them demi-gods. The divine parents of Protectors were punished for disobeying the command of Olympus, and were thus Mechanised, becoming Guardians. Having been born, they were kept in hiding, but soon discovered and almost killed. Ultimately, the Protectors were crystallised into Crystals which can be used by the Lights.
Following the Maker's final act of creating humanity, some gods grew wary of the nature of humans and so 10 gods were sent to Lux to see how these humans behaved. However, the longer that these gods stayed with humans, the more they realised that humans do not seek the same glory that the gods do. Of these 10 Gods, 6 developed romantic love with humans. Equally, one god - Prometheus - fell in love with humanity in general, seeing their simple nature and given his infertility he saw them as his children. The gods who fell in love with humans wanted to take their human loves back to Pantheon and be with them, however, it was instantly forbidden by most of the Gods. Thus, these gods - who would later become the Guardians - decided to procreate with their human loves against the wishes of Olympus, as an act of rebellion.
When the children were born, they were hidden from the view of Pantheon for some years by the collective protection of the Guardians and Prometheus, such that no-one knew they existed. Overtime, Prometheus grew to love one human romantically, just as the Guardians had. He revealed to this human the truth of the universe that only the gods knew and gifted him with magic. However, this human was overwhelmed by the knowledge Prometheus had imparted on him and this drove him to insanity, following which he took his own life. In a state of grief, Prometheus summoned a powerful spell to shatter the boundary between Lux and Spirit to enter Spirit and find the soul of the man he loved in the world of the dead. Upon locating his lover, Prometheus took him to Olympus and restores his lover to life by trading him with his own immortality for the human's mortality. He wipes the man's memory of the love he and Prometheus shared since this would retrigger the knowledge and magic that drove him insane to start with. Prometheus sends the man to Oblivion, then returns to Lux to watch over the demi-gods, hoping he won't be tempted by the man again. However, Viha had been watching Prometheus closely since he ruptured the barrier between Lux and Spirit and appeared in Lux to find the demi-gods. He returned to Olympus to inform the gods of their existence, bringing Prometheus and the Guardians with him to await judgment.
The grand council decide that whilst humans cannot challenge them, the children of humans and gods - Protectors - could since whilst they do not possess the immortality of gods (only a greatly extended lifespan), they are capable of possessing the same powers. They thus determine that the children must be executed. However, this causes the Guardians and Prometheus to wage war on the Pantheon in an attempt to save their children. Some Guardians are, however, captured and they are Mechanised as a punishment. This, in turn, causes greater strife and Pantheon fears a great civil war in Olympus. They finally propose to the remaining Guardians and Prometheus that, if these gods prepare to be Mechanised, they will let the demi-gods - the Protectors - to return to Lux. However, two gods shall also be sent to Lux - one to try to kill the Protectors and the other to try to defend them - and they may recruit humans to help them do so. Facing certain defeat, the Guardians and Prometheus agree and Viha and Maudin are elected the gods to go to Lux: Viha to try to kill the Protectors and Maudin (Devi's father) to defend them. This also quells the unrest in Olympus as the remaining gods do not see the Pantheon as directly killing and now leaving it to humans.
When the time comes for the remaining Guardians and Prometheus to be Mechanised, Prometheus reveals to the Pantheon that he has already lost his immortality and is no longer a god, lying and saying he used up his immortality in a failed spell to cloak the Protectors from the vision of the gods. The gods thus decide to kill Prometheus, however, Alexander cannot bear to see his own son endure die, so offers to be Mechanised, so long as his son is sent to Lux along with the other Protectors. Prometheus and the other Protectors then emerge on Lux and go their separate ways, whilst Viha and Maudin begin planning the war for Protectors that over time would lose meaning and become the repetitive cycle of war that the current Lights are caught up in.
Upon meeting Prometheus, Devi gifts the Lights their Light Powers. As part of their Light Trials, the Lights establish what value they fit with. The Protector with whom they shared the most is naturally drawn to that Light and so can be summoned to assist. Equally, each of the Protectors has an elemental affinity, which is garnered from their human parent, e.g. how Shiva's ice affinity stems from the fact her human father was an Eskimo, which matches the Elemental Affinity of their master.
Upon first meeting them, in their moment of greatest peril, Lights must earn the trust of their Protectors - either through proving themselves in battle or through other means. It is later revealed that it is the Saviours - the grandparents of the Protectors - who steer the Protectors to the Lights when there is the greatest need for them since it is most beneficial for the Protectors to help the Lights as this will result in their own survival.
List of Protectors
Ixion is Sky's protector. Ixion's father is the Guardian Odin, thus making his grandfather the Savior Raiden, and his mother was a warrior princess. Ixion's element is Lightning and he represents Strength.
Ixion takes the form of a knight, but can transform into the horse, Slephnir, in Gestalt Mode. His appearance was heavily influenced by Odin from Final Fantasy XIII.
Eos is Lola's protector. Eos' mother is the Guardian Leviathan, thus making her grandfather the Savior Famfrit, and her father was a sailor. Eos' element is Water and she represents Fluidity.
Eos takes the form of a fairy, but can transform into a winged dragonfly in Gestalt Mode.
Hashmal is Minim's protector. Hashmal's father is the Guardian Hecatonchier, thus making his grandfather the Savior Titan, and his mother was a tribes-woman. Titan's element is Earth and he represents Courage.
Hashmal takes the form of a feline man, but can transform into bipedal beast in Gestalt Mode.
Shiva is Zero's protector. Shiva's mother is the Guardian Seraph, thus making her grandmother the Savior Asura, and her father was an Eskimo. Shiva's element is Ice and she represents Beauty.
Shiva takes the form of an ice-covered woman, but can transform into a motorbike in Gestalt Mode.
Garuda is Storm's protector. Garuda's father is the Guardian Fenrir, thus making her grandmother the Savior Valefor, and her mother was a pilot. Garuda's element is Air and she represents Agility.
Garuda takes the form of a bird-like humanoid woman, but can transform into an organic-looking aeroplane.
Ifrit is Agni's protector. Ifrit's mother is the Guardian Brynhildr, thus making his grandfather Phoenix, and his father lived near a volcano. Ifrit's element is Fire and he represents Anger.
Ifrit takes the form of a beast like man, but can transform into a chariot.
Prometheus is Devi's protector. Unlike the other protectors, he is not a demi-god, but is in fact a true God. He wished to see Humans and Gods interact more. As a result, he took the power of magic from the Gods and distributed it to the humans - a crime for which he was to be destroyed. To try to save him, his father, the Guardian Alexander, offered to be Mechanised, to allow his son to live. The Gods, thus, made Prometheus a Protector - a human-like form with accented god-like powers - and transformed Alexander into a Mech. Alexander's father, the Savior Bahamut, has, since, always hated Prometheus, and even his mother, the Light Goddess Ultima, for what happened to Alexander, such that he exiled them from Pantheon.
Prometheus's is a non-elemental and he represents Justice. Prometheus appears to be an old man, but can transform into an eagle in Gestalt Mode.