Leafpool

Medicine cat of ThunderClan, until she gets fired for breaking the code (but then gets rehired again). The story is told from Leafpool's point of view in all six books of the The New Prophecy arc, as well as part of the prologue of Sunrise and the novella Leafpool's Wish. Even when the story is not being told from her point of view, she still has an important position in the Clan and often plays a central role in the plot and interacts with whomever is currently narrating. In other words, she's a main character.

What you really need to know about Leafpool is that she has an intense, romantic, passionate affair with WindClan tom Crowfeather, which is unacceptable in the Clans because medicine cats are not allowed to have a mate or kits. The two are forced to part ways after eloping/running away together and then coming back after about a day, but complications arise when Leafpool turns out to be pregnant and has to give birth to her kits in secret. Her sister Squirrelflight raises them for her, without telling ThunderClan they aren't really hers, so when that secret is inevitably spilled, Leafpool's life is pretty much ruined. But it all works out in the end, because no one really cares and she just goes back to her job anyway.

Outside of her romantic history, Leafpool is known for being an exceptionally skilled medicine cat. She has a deep connection with StarClan, and is pretty much their Chosen One in some regards because she gives birth to, like, the most important cats ever (did I mention her kits are part of a prophecy that states they will have more power than StarClan?). She also discovers the Moonpool when the Clans arrive at the lake, and has an official celestial guardian in former medicine cat Spottedleaf, who used to be in love with her father (a bit awkward, but not to Leafpool).

In terms of personality, Leafpool is shy, caring, usually a cutie, and sometimes very depressed given her troubled past. She maintains a close bond to her sister, Squirrelflight, and the two of them share rather vague freaky powers in which they can sense each other's emotions and physical sensations from incredible distances. Yeah.