One of the designers of the CommonLispObjectSystem (CLOS). He designed the CLOS MetaObjectProtocol that is described in his book TheArtOfTheMetaObjectProtocol (with Jim des Rivieres and Daniel G. Bobrow). He currently works on AspectOrientedProgramming and is leader of the AspectJay project (see http://AspectJ.org/).
He is currently teaching a MOOC course on systematic software design for beginner programmers using Racket: http://www.coursera.org/course/programdesign. This course is a good for a proper introduction to Lisp as well.