Temperance Brennan is an anthropologist who writes about the character Kathy Reichs in her spare time. In real-life, Kathy Reichs is an anthropologist who writes about the character Temperance Brennan.
In the pilot, Temperance says the next closest forensic anthropologist after her is in Montreal, one of the places the original novels are set.
Angela's father is played by ZZ Top member Billy Gibbons, and there have been several indications that the audience is supposed to understand that her father IS Billy Gibbons (albeit a fictional version of Gibbons, since Angela is fictional). Although Angela's dad has never been given a name, before his first appearance Angela told her friends that her father is famous enough that they might recognize him immediately, and during Gibbons' appearances, there have been several references to the music of ZZ Top.
Caroline Julian, played by Patricia Belcher, is the only guest star to appear in every season
Emily Deschanel's sister, Zooey, appeared on season five, episode ten, "The Goop on the Girl". She appeared as Brennan's cousin Margaret from Wisconsin.