John Sellars is a lecturer in Philosophy at Royal Holloway, University of London. He's a foremost expert on ancient philosophy and Stoicism in particular.
He's the author of Hellenistic Philosophy, The Art of Living: The Stoics on the Nature and Function of Philosophy, and Stoicism. In addition to his academic work, Sellars has published Lessons in Stoicism. A fine introduction to the philosophy that has been translated into several languages.
And if you'd like something else to read after finishing those works, Sellars will be publishing a study on Marcus Aurelius this year.
He's an excellent fit for the Stoa Conversation series and is someone who I've wanted to have on for awhile now.