Cliff Berg is an author of "Agile 2: The Next Iteration of Agile" (Wiley). He is a DevOps instructor and practitioner, and was an early adopter of Agile in 2000 when he was CTO and co-founder of a 200 person IT services company.
I am an Agilist. The company that I co-founded in 1995, with almost 200 employees by the year 2000, adopted eXtreme Programming (XP) that year. My 2005 book High-Assurance Design interpreted secure and high reliability engineering practices in an Agile context, proposing a concrete answer to the question, “How can organizations build highly reliable and secure systems using Agile methods?” Since then I have helped more than ten large organizations to move to Agile and DevOps approaches.