Valaquenta
Account of the Valar and Maiar according to Elvish lore
While those Ainur who have gone into the world are working to make it habitable, let's sort out some definition. The world that they're working on is called Arda, on which Middle-earth is the central continent. There is another continent to the west called Aman, on which the Undying Lands are located. Now that we've covered where the action's at, let's meet the players.
Of the Valar
The Ainur who went into the world can be divided into two groups: Valar and Maiar. The fourteen strongest Ainur are called the Valar, the godlike Powers of Arda. There are fourteen Valar, seven guys and seven gals, and while we'll go over each of them individually, here's a quick prelude. Warning: incoming name dump, but it cannot be helped. The guys are named Manwe, Ulmo, Aule, Orome, Mandos, Lorien, and Tulkas. The gals are Varda, Yavanna, Nienna, Este, Vaire, Vana, and Nessa. We no longer count Melkor as one of the Valar, as he is a jerk.
Manwe and Melkor are basically siblings, if angelic spirits that were all created at the same time can be siblings, but while Melkor is the mightiest (or at least he was in the beginning), Manwe is the best at understanding Iluvatar's plans. Manwe is the king of the world, and he likes air, wind, and birds.
With Manwe dwells Varda, the Lady of the Stars. She is indescribably beautiful, her face glows with the light of Iluvatar, and Melkor hates and fears her. On a typical day, she'll be with her husband Manwe, sitting on their super tall mountain in Valinor and watching the whole world. She is also known as Elbereth, so when anyone in the Lord of the Rings starts saying that name, this is who they're talking about. The Elves clearly love her.
Ulmo is the Lord of Waters. He lives alone. He has been great friends with Manwe ever since the invention of clouds, although he is a bit of a loner and doesn't typically hang around with the other Valar unless it's for something important. Still, he keeps Arda in his thought, and even when the Elves and Men were under the wrath of the other Valar, he never abandoned them.
Aule is next in power, behind Ulmo. His domain is the earth, and he is a great smith who loves gold, gems, and stone. The Noldor, who will be introduced in a few chapters and will be important later, learned a lot from him and were his friends. He was similar to Melkor in that both of them liked making new things, but while Aule wasn't jealous of the works of others, Melkor was hateful and envious, as you may have noticed.
Aule's spouse is Yavanna, the Giver of Fruits. She loves all growing things, from the tallest trees to the smallest mosses. When she isn't wearing her human or elf body, she typically likes appearing as a tree. She really loves her trees.
Mandos is the keeper of the Houses of the Dead. He summons the spirits of the slain and forgets nothing, and while we don't learn much about him, it can be assumed that he's the calm and stoic type of death god rather than the 'let's murder people' type of death god. His wife is Vaire the Weaver, who spends her time weaving tapestries that show the history of the world. She hangs them all over the Houses of the Dead, so the dead have a lot of pretty pictures.
Lorien, Mandos's little brother, is the master of visions and dreams. He has a nice garden, and that's about all we ever learn about him. His wife is Este the gentle, who heals hurts and weariness and gives the gift of rest. Everyone in Valinor goes to her and her husband's gardens for refreshment, and even the other Valar like to go there for rest after a particularly stressful day.
Mandos and Lorien have a sister, Nienna, who dwells alone. She mourns for every wound that Arda has suffered, and teaches others about pity and endurance in hope. She is often found in the halls of Mandos, where she brings strength and wisdom to the spirits of the dead.
The greatest in strength and deeds of prowess is Tulkas, who came last to Arda to help the other Valar in fighting Melkor. He loves wrestling and his favorite weapons are his own two fists. He laughs always, whether in sport or war or in Melkor's face, and while he's not good at giving advice, he is a hardy friend. He is married to Nessa, who likes dancing and who will never be mentioned again.
Orome, Nessa's brother, is a mighty lord. If he's less strong than Tulkas, he is more dreadful in anger. He loved the lands of Middle-earth, and when other Valar went to the Undying Lands, he came last and unwillingly. His likes include forests, hounds, and hunting Melkor's monsters. His wife is Vana, Yavanna's (the goddess of trees) little sister. Vana will also never be mentioned again.
Of the Maiar
Aside from the Valar, a number of less-powerful Ainur had also come into the world. These are known as the Maiar, and they are the servants and helpers of the Valar, although both are the same 'species' of angelic spirits. We don't get to meet many of the Maiar since they don't often take physical form, but there are a few that are worth mentioning. The two that Elves and Men care most about are Osse and Uinen.
Osse works for Ulmo (the god of the oceans), and while Ulmo spends most of his time in the deep ocean, Osse frequents the coasts. He loves storms and laughs whenever he starts one up, which should give you a decent idea of the type of guy he is. His wife is Uinen, who is a lot better received by people, as she is able to calm her crazy husband. She loves sea life, her hair spreads through all the waters of the world, and the Numenoreans, who we haven't met yet but who will be important later, loved her and held her in reverence equal to the Valar.
Melkor hated the sea because he could not subdue it, and it is said that during the making of Arda he tried to sway Osse to his allegiance, promising to give him Ulmo's realm and power in return. Uinen, having none of this, talked some sense into her husband and got him to stop, and Osse has remained good ever since. Well, mostly good. He does still kick up the occasional storm just for the fun of it, so while those who live near the sea may love him, but they do not trust them.
Melian was another Maia who tended the gardens of Lorien before she came to Middle-earth. She will also become important, but not until later.
The wisest of the Maiar was Olorin. He went often to the house of Nienna (the goddess of pity and tears) and learned pity and patience from her. In later days he became a friend to all the people, and took pity on their sorrows, and those who listened to him awoke from despair. You may know him by the name of Gandalf.
Of the Enemies
Last of all we must discuss Melkor, He who arises in Might. Since that name sounds too fair for such a foul fellow, most folks instead call him Morgoth, the Dark Enemy of the World. He had been given great power by Iluvatar, but he turned to evil and squandered his strength in violence and tyranny. A typical villain, he wanted to rule Arda and take over the realms of his peers. He wanted everything for himself alone, and became an arrogant, shameless, pitiless jerk with contempt for everyone except himself.
In spite of the fact that he was not that nice of a guy, several Maiar did serve him, either because they had been loyal to him since his days of greatness or because he later corrupted them with lies and treacherous gifts. Some of the more dreadful Maiar on his payroll were the fiery demons known as Balrogs.
Among those of his servants that people have named, the greatest was Sauron. In the beginning he was a Maia of Aule (the god of smithing), but upon joining up with Melkor/Morgoth, he helped his new master with all his evil plans. Indeed, he was only less evil than his master because for a while, he served another rather than himself. But eventually, Sauron decided to become Morgoth 2.0 and walk behind him on that same ruinous path into the void.