Among the allied-color and enemy-color minor gods of Theros, one of the latter takes on the role of one of the most familiar mythological archetypes in the real world. Every student of folklore is familiar with Thor, the Norse hammer-wielding monster-slayer, and Zeus, the king of the Olympians in ancient Greece who is only half-represented on Theros by Heliod. In point of fact, just about every culture in the ancient world turned to an often-male, angry and boastful deity who was also brave and kind to the weak to explain bad weather. The Vikings had Thor, the Greeks had Zeus, the Japanese had Susanoo, the Phoenicians had Tarhunt, and Theros has Keranos, the blue and red god of storms.
Keranos is mentioned briefly in the background lore - in one of the Planeswalker's Guide to Theros articles it's noted that Cymede, queen of Akros and wife to Anax, with whom she shares her card, is a worshipper of the storm god, from whom she purports to receive prophecies of what the Akroans should do in their latest battles. It's fair to assume that she's not the only Akroan who favors Keranos - and the lightning-lit mountaintops of the polis are the perfect place to worship a storm god.
Of course, Keranos is also a god of sudden inspiration, as the flavor text of Steam Augury describes:
Keranos is a fickle god, delivering punishment as readily as prophecy.
Though there are no Theros cards named after him, he is name-checked in another flavor text - naturally, that of Lightning Strike:
"The hand of Keranos can be seen in every rumbling storm cloud. Best not to stand where he points." - Rakleia of Shrine Peak
Shrine Peak is probably the location of Keranos's principal temple, and that may be in or around Akros. We also see the literal hand of Keranos in Lightning Strike's art - if he is any of the faces in Steam Augury, and judging by that cloud-formed arm, he will take human appearance like most of the other gods of Theros.
In mechanical terms, a god of storms and prophecy probably interacts a lot with instants and sorceries, perhaps copying or recurring them, or perhaps having an Epic Experiment-like effect. In that respect he has some relation to the Izzet guild of Ravnica.
It's hard to tell what Keranos's relations with the other gods are like, though it's hard to believe he'd be on necessarily bad terms with any of them; his similarly volatile personality to Purphoros's might make the two of them quite friendly.