While many people could lay claim to the title of "father of digital marketing", Philip Kotler is most likely the person you're thinking of. He is a professor at Northwestern University's Kellogg School of Management and has written extensively on the topic, including in books such as "Marketing 4.0" and "Blogging for Profit". Kotler also founded two well-known companies in digital marketing - one that provides e-mail marketing services and another that specializes in online advertising. His insights into modern-day marketing have led him to be an influential voice in the industry, and his teachings continue to shape how businesses do business online today.