Huitzilopochtli

Huitzilopochtli, Aztec God of War and The Sun. Big Bad of Season 3.
Charming, bold and adventurous with a great belief in prophecy. His outward charm belies a being of incredible determination and ambition to overthrow the 'Others' (Primordials) and recreate the world without the weakness of mortals and lesser Gods and Scions. Capable of breath-taking acts of cruelty and violence.
First appeared in Season 3. Died in Season 4.
Season 3
Huitzilopochtli prophecised about the arrival of a being known as the 'Warchild' for hundreds of years. With the birth of Fionn and Apate's child on the battlefield of Tartarus his prophecy had arrived. From the moment of his birth he took an intense interest in Ford. Huitzilopochtli saw him as a being with the potential to outlive the 'Others' that ravage Earth and overthrow them. However, for the safety of Apate and Ford, Eddie Eckstein put them into the future and beyond Huitzilopochtli's reach. He patiently waited for Ford's return, believing in the surety of the prophecy of the Warchild.
His patience paid off when Ford was dragged back through time by Legba. Though Ford was intent on vegenance against the Olympians he was drawn into a deadly battle with Tartarus. When he finally killed Tartarus it heralded the second part of the prophecy- the breaking of the seal of the Others- and resulted in a black hole opening on the edge of the Solar System. Huitzilopochtli was delighted at this development for it signalled that the test of the Gods would soon be at hand- and he was confident that he would last it.
He called Ford to his domain a number of times but was frustrated by Ford's busy schedule. Eventually he sent his trusted House member Tlazolteotl, the Atzlanti Goddess of Filth, to 'bless' Ford's bed with a spell of lust and entreated him to come visit. Ford visited with him and found him to be a very gracious host and appreciated that he said he was committed to lasting peace. Ford was impressed by the depth of his knowledge of the metaphyics of the Gods and was intrigued by the insight of his prophecies. Nevertheless he rejected the notion of the prophecy and his place within any plan. 'H', as Ford had taken to calling him, told him it was prophecised that the Warchild would reject him. At least at first. Despite sensing that H was more hardline than he thought he could ever be Ford left him on good terms.
After Ford had resolved his vegenance against the Olympians, without resorting to killing Ares, H offered his congratulations- but expressed his misgivings that Ford hadn't done what was necessary. Behind the scenes he personally killed six of Ares scions at the farm-house to bolster his own strength.
Still H watched with pride as Ford racked up victory after victory- rescuing his father, surviving encounters with Chronos and Chaos- calling them proof of his 'magnificence' and evidence that with Ford at his side he would outlast the coming cataclysm. H dropped his mask somewhat and told him outright that Ford should pull away from his weaker friends who would surely perish and step up to his destiny. H reminded him that the breaking of the seal was, after all, his responsibility. Ford couldn't abide abandoning his friends and rejected Huitzilopochtli's design.
After Hope had awoken she was alerted to the deadly interference of Chronos and Chaos and the future calamity they presented. She spoke with Athena about an artefact that existed that could close the portal. Ford went on a mission to retrieve the artefact and eventually recovered tracked it down to the Temple of the Djinn; the Shield of Gaia. With Hope by his side, and the rest of his House behind him, he harnassed the shield's power and directed it at the portal. The portal was closed for ever. Ford and the others threw a gigantic party.
Huitzilopochtli was incandescent with anger that the portal had been closed. Ford had robbed him of his greatess challenge. He immediately set forth to re-open the portal. Knowing that the God of Tartarus had fused with Jordan Swan he sought to lure the former-Centurion to his side and to sacrifice him to re-open the portal. He knew he would have to discredit the softly-softly approach of Ford and to draw Jordan to meet with him to help him control his Aspect. To this end he divinely inspired visions of the butchery of Ares' scions at the farmhouse in Jordan to make him believe he was responsible during one of his blackouts. H's plan was challenged when Ford, with the assistance of Hope, stayed with Jordan all night and comforted him. It was destroyed when Bonnie Dankbars, who had much earlier come across the bodies, had used her newfound powers to communicate with the dead and had discovered that Huitzilopochtli was responsible.
Ford saw Huitzilopochtli for what he was and went to draw his friends close. Huitzilopochtli, knowing his first plan had failed, acted quickly in retaliation. He struck out on mutilple fronts to sow disorder, reaching out to Hel and Kalfu to aid him, and to increase his own power through murder. He swiftly murdered Demeter by way of a lethal pommegranate.
Realising that it was Ford's abiding belief in his self-determined aspect of 'Hope' that was frustrating his plans, and the narrative of his beloeved prophecy, he sought to bring Ford to heel by killing Hope and crushing his spirit. He kidnapped Hope, severly injuring the Sisters of the Whip (Agony, Ava and Selena- who Ford had entrusted to protect her) in the process. Meanwhile he instructed Hel to strike at Asgard when the time was right. 
Ford, having called a meeting of House Corvin, was busy dealing with this barrage of developments when he was alerted to the kidnapping of Hope. He immediately called for a rescue party to be formed and left on the Rio with dozens of his friends and allies.
They arrived in Huitzilopochtli's realm to discover that tens of thousands of warriors were sacrificing themselves for the glory of Huitzilopochtli and madness was in the air.
Murdered Hope.
Crippled in his fight with Ford. 
Placed in Pandora's Box.
Season 4
Died in the Abyss of Pandora's Box.