Paul Graham (born 13 November 1964  ) is an English computer scientist, venture capitalist, technology entrepreneur and essayist. He is best known for co-founding Y Combinator, the world's most powerful seed accelerator, his work on Lisp, for co-founding Viaweb (which eventually became Yahoo! Store). He is the author of some programming books, such as: On Lisp (1993), ANSI Common Lisp (1995), and Hackers & Painters (2004).
In 1996, Paul Graham and Robert Morris founded Viaweb, the first application service provider (ASP). Viaweb's software, originally written mostly in Common Lisp, allowed users to make their own Internet stores. In the summer of 1998 Viaweb was sold to Yahoo! for 455,000 shares of Yahoo! stock, valued at $49.6 million.  At Yahoo! the product became Yahoo! Store.
Graham later gained fame for his essays on his website paulgraham.com. Essays he wrote covered topics ranging from "Beating the Averages",  which compares Lisp to other programming languages and introduced the hypothetical programming language , to "Why Nerds are Unpopular",  about nerd life in high school. A collection of his essays were published as Hackers & Painters by O'Reilly, which includes a discussion of the growth of Viaweb and what Graham perceives to be the advantages of Lisp to program it.
In 2001, Graham started working on a new dialect of Lisp named Arc. Since then, he has written many essays about the language, and some internal projects at Y Combinator have been written in Arc, most notably the Hacker News computer science web forum and news aggregator program.
In 2005, after giving a talk at the Harvard Computer Society later published as "How to Start a Startup", Graham along with Trevor Blackwell, Jessica Livingston and Robert Morris started Y Combinator to provide seed funding to a large number of startups, particularly those started by younger, more technically oriented founders. Y Combinator has now invested in more than 400 startups, including Justin.tv, Xobni, Dropbox, Airbnb and Stripe. 
Graham graduated from Cornell University with a Bachelor of Arts in philosophy in   1986.  He then attended Harvard University, earning Master of Science (1988) and Doctor of Philosophy (1990) degrees in Computer Science.   He has also studied painting at the Rhode Island School of Design and at the Accademia di Belle Arti in Florence.  
Graham's hierarchy of disagreement
Graham proposed a "disagreement hierarchy" in a 2008 essay "How to Disagree",  putting types of argument into a seven-point hierarchy and observing that "If moving up the disagreement hierarchy makes people less mean, that will make most of them happier." Graham also suggested that the hierarchy can be thought as a pyramid, as the highest forms of disagreement are rarer.
Following this hierarchy, Graham notes that articulate forms of name-calling (e.g. "The author is a self-important dilettante") are no different from crude insults.
The Blub paradox
Graham considers the hierarchy of programming languages with the example of "Blub", a hypothetically average language "right in the middle of the abstractness continuum. It is not the most powerful language, but it is more powerful than Cobol or machine language."  It was used by Graham to illustrate a comparison of power between programming languages that go beyond Turing completeness, and more specifically, to illustrate the difficulty of comparing a programming language one knows to one that one does not. 
Graham considers a hypothetical Blub programmer. When the programmer looks down the "power continuum", he considers the lower languages to be less powerful because they miss some feature that a Blub programmer is used to. But when he looks up, he fails to realise that he is looking up: he merely sees "weird languages" with unnecessary features and assumes they are equivalent in power, but with "other hairy stuff thrown in as well". When Graham considers the point of view of a programmer using a language higher than Blub, he describes that programmer as looking down on Blub and noting its "missing" features from the point of view of the higher language. 
Graham describes this as the "Blub paradox" and concludes that "By induction, the only programmers in a position to see all the differences in power between the various languages are those who understand the most powerful one."