He's been a controversial figure in many forums but his emacs lisp tutorial is the best out there. I gave him a donation through Paypal (for approximately the price of an O'Reilly book) and he personally sent me an email thanking me.
He does imperative programming in Lisp:
(let (a b result)
(setq a 1)
(setq b 2)
(setq result (+ a b))
result)