What makes a programming language popular?

At any given time, a programming language can usually be thought of as
currently fashionable, rising in popularity, or losing popularity. I would
like to hear some thoughts on what makes a language popular, what brings it
back into popularity, or what might be the "marketing" strategy for anyone
who cares about their language making an impact and achieving wide use.

This is, of course, disregarding whether being a popular language is a good
thing or not. :-)

Aaron W. Hsu | arcfide@xxxxxxxxxxx | http://www.sacrideo.us
Programming is just another word for the lost art of thinking.