No, there were many before here. Here is a list of the Thunderclan medicine cats mentioned in the Warriors series so far.
Leafpool became a warrior after she lost her status as Medicine cat because she is too young to join the elders and felt she could no longer be a medicine cat because everyone knew she had kits.
She forgives Hollyleaf, then steps down as ThunderClan's medicine cat, as she feels she can no longer continue. Jayfeather will be ThunderClan's medicine cat in the next series.
Jayfeather is still only the apprentice, even though he has his full name. They can both be medicine cats. Leafpool self-exiled herself after Hollyleaf told everyone their secret at the gathering.
No. She will come back to ThunderClan and return to being a medicine cat.
Hollyleaf's and Lionblaze's mother is Leafpool, a ThunderClan medicine cat. Leafpool has three kits with Crowfeather: Hollyleaf, Lionblaze, and Jayfeather.
If you're asking who Leafpool is, then Leafpool is a light brown tabby she-cat with amber eyes. She becomes ThunderClan's medicine cat in the 2nd series 5th book which I forgot the name. Leafpool's mother and father are Firestar and Sandstorm. Her sister is Squirrelflight. Her mate was recently Crowfeather from WindClan and her kits are Hollyleaf, Jayfeather, and Lionblaze. Leafpool's apprentice is Jayfeather and Leafpool's mentor is Cinderpelt. Leafpool later quits being a medicine cat and becomes a warrior while Jayfeather takes over as medicine cat.
He was scorned by some, yes, but not openly punished by Onestar. How do you know?
Leafpool did leave the clans with Crowfeather, but then she came back while her clan was under a badger attack, and took Cinderpelt's spot as a medicine cat when Cinderpelt died saving Sorreltail's kits.
Leafpool is ThunderClan's former medicine cat. She resigned from her duty and became a warrior because she believed she could no longer be a medicine cat, since she had broken the warrior code. Jayfeather is one of Leafpool's sons and her former apprentice. He is know the full medicine cat and is one out of three cats in the prohecy. He is blind and has no apprentice. He can read other cats' minds and can walk in other cats' dreams.
In Sunrise, Leafpool resigned her position as medicine cat, saying that she was no longer worthy to serve as the medicine cat of Thunderclan. However, whether she is still a medicine cat as of series 4 is not known for sure.LEafpool still knows all of the things needed to become a medicine cat, but resigns after admiting that she had kits with crowfeather. Jayfeather remains medicine cat in "Omen of the Stars"
In the Warriors series by Erin Hunter, the three cats are Hollyleaf, Jayfeather, and Lionblaze. Their mother is Leafpool, a medicine cat from ThunderClan.
Firestar's daughter is Leafpool and his half-son is Brambleclaw. Leafpool is a medicine cat in ThunderClan and Brambleclaw becomes the leader of ThunderClan, taking the name Bramblestar. Both cats play significant roles throughout the series.