Arastoo Vaziri (Season 4–) is a temporary lab assistant first appearing in the episode "The Salt in the Wounds". Originating from Iran, he is a devout Muslim and prays five times a day. Expecting others would find it odd that he is both a scientist and very religious (a suspicion his co-workers later confirmed), Vaziri decides to put on a false accent to sound "fresh off the boat" and thus make his religious devotion seem like an irrelevant byproduct of his heritage. In season 5 episode "The Beautiful Day in the Neighborhood" he slips up, and his secret is revealed to the team (and the audience). When asked if she noticed anything strange about Arastoo's accent, Brennan says she thought it was odd that an Iranian would speak English with a Jordanian accent, but she felt that was his business. Dr. Sweets helps Arastoo work through these issues.
In the season 5 episode, "Devil in the Details," Vaziri says he served as a military translator in Iraq, where he killed an insurgent while defending his life after surviving an IED. His fellow passengers did not survive. What is not explained is why Vaziri, from Iran, would serve as an interpreter in Iraq. Iranians speak Persian, whereas Iraqis speak Arabic, although it is possible he is trilingual. It is unclear if the writers meant Afghanistan (where Persian would have still been of use as they speak a Persian-related Dari or Pashto), or if the writers are retconning Vaziri as a speaker of Arabic rather than a Persian. It's quite possible that Arastoo is multi-lingual, speaking Persian, Arabic, and English. While the language spoken at home while he was growing up would most likely have been Persian or English, as a devout Muslim he would probably have some knowledge of Arabic anyhow and it is entirely possible that he studied Arabic academically.
In the fourth-season finale, Arastoo was re-imagined as a potential buyer of Booth and Brennan's night club.
In the sixth-season premiere it is revealed he switched majors from Forensic to Cultural Anthropology and is interning at the Baghdad Museum. He returned in The Bones that Weren't.
In The Pinocchio in the Planter, Wendell mentions that Arastoo comes from a wealthy family.
He played a fairly major emotional role in the season 8 episode 6 The Patriot In Purgatory. He made a speech of the 9/11 terrorists religion and his. “This was not the work of religion. It was arrogance. It was hypocrisy. It was hate. Those horrible men who hijacked those planes hijacked my religion that day, too. They insulted my God. So no, this isn’t too difficult. It’s a privilege to be able to serve this victim, to show him the care and love that was so absent that day,”
In The Bod in the Pod it is discovered that he writes poetry in Farsi and at least one of the poems is dedicated to Cam. At the end of that episode we also find out they started seeing each other some time recently.
The poem Arastoo recites, translated, goes something like this (and let me assure you is not like the fake translations in some of the chatrooms) -- this translation was done by a native Persian speaker.
I worship love,
Not as in writings
gave up my only belief,
annihilated my existence,
and her heartbeats my essence
I am in paradise from now on,
With you my sweetheart.