There was never any reference to Firestar's Twoleg's name.
Thornclaw
No. That is a Twoleg name.
It is about Firestars grandchildren and their adventures.
Cloudtail (cloudkit/paw)
He was hit by a twoleg monster. (Monsters means cars)
His fathers name is jake and his mothers name is nutmeg.
Their is no specified time. He would of probably been there at the birth.
Graystripe met Millie at a Twoleg's place when he was captured by Twolegs.
In the "Warriors" series by Erin Hunter, the term "twoleg" refers to humans. Twolegs are the creatures that the cats in the series encounter and interact with, often causing trouble or posing threats to the Clans. In the specific instance you mentioned, the twoleg causing harm to the cats is likely a human engaging in activities that endanger the lives of the cats in the story.
Warriors: Power of Three: Book 5: Long Shadows
Firestars Quest, BLuestars Prophecy, and Skyclans Destiny..There are also the manga books.
His mentor was originally Longtail, but when he got blinded his mentor became Thornclaw.