Died of suffocation while buried alive in a coffin in Pine Valley's Memorial Park [Jul 4, 2006]
Doctor specializing in fertility
Single (presumably a widower)
Emily Madden (presumed deceased)
Raised Josh as his son
Implanted Erica's aborted embryo into his wife Emily 
May have been involved in the hit-and-run death of newspaper reporter Meredith Wilson to silence her inquiries in illegal adoptions [Date Unknown]
Lied to Julia Santos about the results of her fertility tests 
Hospitalized after a suspected heart attack induced by poisoning [winter/spring 2006]
Dr. Greg Madden first encountered Erica Kane and her new husband, Jackson Montgomery, on their honeymoon. Erica got the distinct feeling that she knew Greg from somewhere, which Greg denied. Greg later showed up in Pine Valley, where he encountered Erica again. Greg, a fertility specialist, explained to Erica that he was opening a clinic in town. Erica still could not shake the feeling that she knew him from somewhere.
Greenlee Lavery demanded that Greg give her the sperm of her husband Ryan, which was housed in the clinic that Greg bought. Greenlee explained how Ryan had a vasectomy, so his frozen sperm was the only means to impregnate herself with his baby. Greg refused Greenlee's request, citing legal reasons.
Greg eventually used Ryan's sperm to impregnate Kendall. Shortly after, it was revealed that he was the doctor who had performed Erica's abortion years ago in New York. Unfortunately for Erica, he hadn't disposed of the fetus -- he had implanted it into the womb of his barren wife, Emily, and his son Josh was actually Erica and Jeff's son. He was also the doctor who had treated Dixie Cooney in Switzerland years earlier, and had convinced her to give her baby girl up for adoption when it was born.