The British-born Sullivan was described recently by Tyler Cowen as the US’s “most influential public intellectual” of the past 20 years. That may be hyperbole, but Sullivan’s influence on key debates, particularly on the US federal government’s recognition of same-sex marriage, has been immense. Sullivan, a conservative, first made the case for gay marriage in the late 1980s and kept it on the agenda. Today, 36 states have legalised gay marriage. Sullivan was also a pioneer of political blogging.

Further reading:

Andrew Sullivan's Twitter

Andrew Sullivan's (former) blog

Here Comes The GroomSullivan presents the conservative case for gay marriage.

Who is the most influential public intellectual of the last twenty-five years? Tyler Cowen argues for Sullivan's importance as a public intellectual.