What was the form of the Prophet's hair (peace and blessings be upon him), and what are the forbidden hairstyles?

The Prophet's hair, may Allah bless him and grant him peace, was neither too curly nor too straight. It reached his earlobes, or between his earlobes and his shoulders, and sometimes it touched his shoulders. He would dye his hair with henna and katam (a plant used for dyeing). He would part his hair after having let it hang loose, and he performed Hajj with his hair matted. Perhaps he would braid his hair while traveling.

As for forbidden hairstyles, they include al-qaza', which is shaving part of the hair and leaving part of it, imitating disbelievers or transgressors, and imitating the ignoble among people.