Wikipedia:Naming conventions (common names)

Convention: Use the most common name of a person or thing that does not conflict with the names of other people or things.

As to names of persons, there are two schools of thought: use the most commonly used name, or use the person's full name. After a vote among those interested, we've come down in favor of the former. Names of persons should be the most commonly used name for the following reasons:

We want to maximize the likelihood of being listed in other search engines, thereby attracting more people to Wikipedia. Also, the Jimmy Carter page has the string "Jimmy Carter" in the page title. This is important because other search engines will often give greater weight to the contents of the title than to the body of the page. Since "Jimmy Carter" is the most common form of the name, it will be searched on more often, and having that exact string in our page title will often mean our page shows up higher in other search engines.
We want to maximize the incidence of accidental links.
Using full formal names requires, if one wants to link directly to the article, both that people know the full formal name and that they type it out, both of which are a royal pain. If one links to a redirection page, there's the messy "redirected from" announcement at the top of the page.

Examples of common names that should be used instead of formal names are: George W. Bush, Bill Clinton, Al Gore, Mozart, Bach, Goethe. Middle names should be avoided unless they are the most common form of a name (as in, say, John Wilkes Booth). Names with initials should have spaces after each period as in normal English text, for example, H. G. Wells.