Previously, he was the co-founder of Pacific Square Research and Greenberg Meritz Research & Analytics – both independent, short-biased investment research firms.

Greenberg spent more than 40 years as a financial journalist at some of the country's leading newspapers, websites, and broadcast media, where he covered almost every industry.

He served as senior stocks commentator at CNBC and was financial correspondent at the Chicago Tribune. He also spent 10 years as the daily business columnist for the San Francisco Chronicle, during which time he started his five-year run as Fortune's monthly Against the Grain columnist and was the morning business reporter for San Francisco's KRON-TV.

When the Internet and online media were still emerging, Greenberg was one of the first mainstream journalists to make the shift online, when he became senior columnist at TheStreet. He later shifted to the same role at MarketWatch. When Dow Jones bought out MarketWatch, he added a weekend investor column for the Wall Street Journal to the mix.