Paul Graham is the author of On Lisp (1993), ANSI Common Lisp (1995), and Hackers & Painters (2004). In 1995, he and Robert Morris started Viaweb, the first SaaS company, which in 1998 became Yahoo Store. In 2002 he discovered a simple spam filtering algorithm that inspired the current generation of filters. He has an AB from Cornell and a PhD in Computer Science from Harvard.