Pierce Halley

Pierce was one of George's interns.

History
Pierce and Alex have a mutual dislike for each other. When Alex was trying to decide which intern to give to George, he considered Pierce because he didn't like the name.

Later, after operating on Sadie, Alex told the interns he didn't respect them but Pierce noted that he still respected Izzie, even though she killed a patient.

Romantic
Cristina once considered using him to "scratch an itch", asking Meredith if he was clean, but later decided against it.

Pierce was dating Megan at some point, but they broke up, when she found a nurse's number on him, and then got back together. During their break, Megan slept with Steve, and Steve accidentally sent an email to people about their hookup, including Pierce. According to Ryan, Pierce wants to kill Steve, but it appears that Steve has punched Pierce, with Pierce having a black eye and Steve having a bloody hand.

Seattle Grace: On Call
He still harbors some resentment towards Steve, whom he refers by his last name of Mostow, for marrying Megan, whom he still feels something for. He then urges Megan to take a paternity test to actually confirm whose child it was.

After leaving the hospital, it appears that he briefly hooked up with Graciella Guzman. But the relationship was short lived, as Graciella confronted him, while he was talking to Megan. When she broke up with him, he just brushed it aside casually, and continued to chat with Megan.

Pierce seem unusually happy, when he found out that Megan took the paternity test on Tuesday, and went to Joe's to ask her about the results. When Steve found out about the test, Pierce seemed smug about it, and was actually hoping that he was the father of Megan's child. He then got into a fight with Steve, when Megan opened the envelope containing the results.

Even after the fight and knowing that Megan's baby was Steve's, he still harbors some hope of getting back with Megan, after Steve divorces her. But she is still not too sure about that, and mentioned that she needed time to be by herself, to decide, before saying goodbye to Pierce and leaving Joe's.

It was never revealed what happened afterwards.

Career
Originally one of Alex Karev's interns, he was later reassigned to George O'Malley. He was part of the secret intern society.

During his second year of residency, Pierce was part of the first round of lay-offs when Seattle Grace Hospital and Mercy West Medical Center merged. Pierce is now working in the morgue at Seattle Grace. But he doesn't appear to be too happy about his new job, referring to it as " working in the underbelly of Seattle Grace" and that he hates it.

Notes and Trivia

 * It is possible that the nurse whose number was found, is someone called Samantha, from the OB ward, who is still on good terms with Pierce.
 * He was briefly in a band, formed by Steve, but was kicked out after he made Megan cry, while they were in the midst of a performance.
 * As an M.D. working in the morgue, he's most likely a pathology intern, since he stated he no longer holds "resident" status.