Ross Geller is Monica's older brother. He works as a paleontologist. He was put on sabbatical when he freaked out after someone ate his sandwich, and never returned there. He now teaches at New York University.
Ross has technically been married three times, but only lived with one of his wives (during their marriage). His first wife was Carol. They dated in college and later married. They were married for four years, until Carol realized she was a lesbian. However, Carol got pregnant right before the divorce, and gave birth to Ross' son, Ben, now nine years old.
Ross' second love was Julie, who he actually met in grad school. They worked together on a dig in China. They broke up when Ross found out Rachel loved him.
Which brings us to Girlfriend Number Three- Monica's best friend in high school, Rachel Green. Ross had a huge crush on her since 9th grade, but they never dated until she found out about his crush. They dated a year, until he slept with someone else during their one-night break and they broke up.
The following year, Ross was introduced to his second wife Emily, ironically enough by Rachel. They got engaged after only six weeks and married in London. Ross, however, said the wrong name during the ceremony and Emily didn't trust him anymore. After spending months trying to get her back, he gave up and they got divorced. Emily is now married again.
While in Vegas, Ross and Rachel got drunk together and ended up getting married. He told Rachel he would get an annulment, but didn’t. They ended up having to get divorced.
Ross' most serious non-married relationship was with Mona, whom he met at Chandler and Monica's wedding. They dated for quite awhile. She stayed with him even though he'd gotten Rachel pregnant. Mona wanted to send out a combined holiday card, but Ross gave her a key to his apartment instead. And then had the locks changed. The final straw for Mona was when Ross didn't tell her that Rachel had moved in with him.
Ross served as Best Man at Chandler's wedding. Six weeks before the wedding, he and Rachel fooled around and she wound up pregnant with his child. She gave birth to his daughter, Emma. The family continued to live together until things got too weird between him and Rachel.
He was thrilled when he met Charlie, a gorgeous palentologist who worked with him at NYU. She, however, hooked up with Joey first. It wasn't until a trip to Barbados that they began dating. Ross and Charlie dated a couple months until one of her ex-boyfriends showed up and they realized they were still in love with each other. FINALLY in the last episode of the series, Ross told Rachel he's still in love with her, hoping she'd decide not to go to Paris. She stayed and they got back together for good.
Did I mention Ross once had a pet monkey named Marcel?