Who is Epsilon and why does it have my data?

If you happen to be a customer of one (or many) dozens of companies–including Citibank, Chase, Capital One, American Express, Walgreens, Target, Best Buy, TiVo, TD Ameritrade, Verizon, and Ritz Carlton, chances are you received an email from them recently letting you know your data was compromised. I wasn’t aware of Epsilon and came across a great write-up recently.