Former Pfizer ($PFE) chemist Ken Koe--responsible for billions in sales--has died at 90, Bloomberg reports. Koe, along with fellow chemist Willard Welch, developed blockbuster antidepressant Zoloft, a med that reached its sales peak in 2004 with $3.36 billion, the news service notes. The pair began developing the product in the 1970s; it eventually won the FDA's green light in 1991, and their team in 2006 took home an innovation award from the American Chemical Society in recognition of its impact. More