As the new king on the block, Stannis has a lot of new faces surrounding him. Here are a few of the key members of his court we were introduced to in the book:
Cressen is Stannis's maester at the beginning of the story. He is very old, having served the Baratheons for years, and he remembers Stannis as a child and is fiercely loyal to him, thinking of him as the son he never had (1.Prologue.134). Seeing Melisandre as an evil influence on his lord, Cressen attempts to murder her with a poisonous glass of wine, but somehow Melisandre manages to survive the toast even as it takes the elder maester's life.
Pylos is Maester Cressen's assistant. He is promoted to Stannis's maester when it is decided that Cressen is too old to fulfill his duties.
Patchface is the court jester of Stannis's court. He gets his name from the tattoos on his face, which are patches of red and green. While traveling to Westeros, the ship he rode on sank, and Patchface washed ashore three days later. Since then, the once witty and clever child has gone mad and can only speak in paradoxical riddles about life under the sea (1.Prologue.41). He is Shireen's constant companion.
Shireen is Stannis's daughter with Lady Selyse. When she was a baby, she became ill with grayscale and now "half one cheek and well down her neck, her flesh [is] stiff and dead, the skin cracked and flaking, mottled black and grey and stony to the touch" (1.Prologue.12). A kind and curious girl, she is the only person who laughs at Patchface and also the only one who cares if he lives (1.Prologue.16). No wonder he stays close.
Lady Selyse is Stannis's wife and Shireen's mother. She is a devout follower of the Lord of Light, and she believes the red comet was sent as a sign for Stannis, suggesting that her husband should kill Renly (1.Prologue.118).
Salladhor Saan is a banker, smuggler, trader, pirate, and the "self-styled Prince of the Narrow Sea" (11.Davos.42). He has joined Stannis's cause and brings news that King's Landing could be easily taken, but his recommendation that they strike soon is not taken up by Stannis. For his services, he wants Cersei to be sent to his bedchambers after the battle. Salladhor also sees through Melisandre's rituals, claiming the sword she gave Stannis is not Lightbringer.
Ser Imry commands Stannis's fleet during the Battle of the Blackwater. While planning the battle, Davos gives him sound advice, but Ser Imry does not heed it since Davos is of low birth (59.Davos.10).
Melisandre of Asshai is the mysterious Red Priestess of R'hllor, the Lord of Light. She comes to aid Stannis and converts Lady Selyse, as well as several of his bannermen, to her religion.
The extent of her power is currently unknown. She has Stannis pull a sword from a burning effigy and claims it is the legendary Lightbringer, a claim Salladhor doubts and which seems unlikely as it burns the king (11.Davos.21). On the other hand, she births two shadow assassins to murder Renly and Ser Penrose, and her power certainly convinces Davos (43.Davos.171).
Why she is helping Stannis is equally mysterious right now. We seem to get a hint, though: When Davos and she are sailing underneath Storm's End, Davos mentions that the gods of shadow protect them. She replies, "Speak not that name, ser. Lest you draw his black eye upon us. He protects no man, I promise you. He is the enemy of all that lives" (43.Davos.156). Melisandre's Lord of Light certainly seems at odds with this god of darkness (whoever that god is), but we have no idea what this has to do with Stannis. Yet.