Annam
Annam the All-Father is the Neutral creator of the giants in the Greyhawk setting and the head of the pantheon of giants.
Father of Giants
As the creator of giants, Annam is a really huge god. Standing up to 100', the Progenitor of Worlds towers above all. Giants believe he created the Prime Material Plane, while others claim he worked alongside the other deities to create the world in cooperation. Storm Giants however believe that all of creation stems from his dreams; that Annam is the godhead of reality. While his creation of the race of giants might have given him the metaphorical title of "Father of Giants", for the rest of the pantheon of giants this is to be taken literally. Annam has a nasty case of being unable to keep the dick inside of the pants: as such he has sired many childen with gods and mortals alike. They are:
Diancastra
Diancastra is the Chaotic Good demigoddess of trickery, pleasure and fertility. She can be recognized by a combination of her green eyes and a streak of green skin along her left shoulderblade. Born from the union of her father and a mortal giantess, she was granted her place amongst the gods through a series of tests given by her father. She won them all: not by force or heroic feats but through guile and wit. One of these tests was to circle the world in less than one hour; she did this by taking a map of the world and walking around it. Everything she does she does for the lulz: from trolling the Seelie Court to stealing from Blibdoolpoolp and the servants of her brother Surtr. Diancastra is a traveling goddess: she does not stay long in one place and lives off her wits, guile and the generousity of her lovers. And while she has no clergy or official worshippers yet, she has started to be invoked by non-evil giants as a fertility goddess; the children that come from a union that involved invoking Diancastra often are just as free-spirited as the demigoddess herself.
Grolantor
Grolantor is the Chaotic Evil god of competition, strength, Ettins and Hill Giants. Originally banished to Carceri by his father Annam for allying with his brother Memnor, the ban has been revoked ever since the All-Father left. Grolantor is a stupid and weak-willed but very strong god who demands that his followers persecute those smaller than them: everything shorter than an Hill Giant/Ettin is fair game. Along the way they willfully deny the fact that the Hill Giants are the smallest of the giant races: to admit weakness is considered anathema to the followers of the Runtherder. He created the Hill Giants by breeding all sorts of crazy shit together: a combination of castoff giants of all races, all sorts of serpentine monsters and even the Hag goddess Cegilune. Ettins on the other hand were created when Grolantor slipped the Dragonlance to a bizarre serpent monster with heads on both ends of her snake-like body. Gorlantor is a hands-off deity: as long as you never admit weakness or fault and you oppress those smaller than you you're fair game: he has no holy days aside from an occational eating contest.
Hiatea
Hiatea is the Neutral Good goddess of Nature, Agriculture, Hunting, Women and Children. Like her sister Diancastra she is the result of a union of her divine father and her mortal mother. Annam originally intended to use magic to ensure Hiatea was female; when her mother learned of this she sent her to be raised by Firbolgs. When her mother died Hiatea learned of her divine parentage and presented herself to her father. Like her sister she was tested; instead she opted to show that she was a warrior to be reckoned with by killing the Tarrasque and presenting its head to her father. He was impressed and elevated her to divine status. She is popular with Firborg and Wood Giants, who hold her in high esteem. There are two kinds of clerics to Hiatea: the community priests (who tend to the land and people) and the protector priests (who patrol the woodlands to protect the community). Hiatea often communicates with her priests and holds that good relations with the neighbouring races (often Wood Elves of some kind) are important. All of Hiatea's priests are required to be able to hunt; during regular hunts and the ritual monthly or annual hunt. Those who cannot are forced to retire.
Domain
Annam is all-knowing and has a degree of foresight. While this would mean a "I win" button for any other god, Annam is a lustful and instinctive individual who often acts against his own interests because "it felt right". He rarely shares his knowledge with his followers: only the greatest may be his clerics and only if they will excel they will receive a vision, once. He rarely sends an avatar to the Prime Material Plane, only when history is defined will the All-Father be there.
Dwelling
Annam used to live in the realm of Gudheim in Ysgard. Here there was his orrery from which he could watch the worlds and their going ons. But he grew tired of watching the countless conflicts on the countless worlds, and eventually left for the Outlands. Gudheim still exists; tended to by the faithful who sometime serve as the hosts to pious clerics of Annam who get to see Gudheim just before they die. The souls of giants who die do not go to Gudheim: instead they go to Jotunheim, which is on Ysgard as well.
Followers
Annam is worshipped by almost all of giantkind, who each see part of themselves in their creator. Annam teaches to honor the hierarchy of the society of giants, not to raise one's hand against a fellow giant (failing this results in immediate forfeit of one's clergial rank) and to not underestimate other races or impede their goals. Annam's clergy is ranked high in giant society, but they have to be of the line of the elder giants in order to qualify for this position. As said before, they receive at best once in their lives a vision from their god, but far from all of them do so.