I was going to say I've never seen him identified as "co-founder" in a headline rather than just "founder".
Wikipedia was formally launched on 15 January 2001 by Jimmy Wales and Larry Sanger, using the concept and technology of a wiki pioneered in 1995 by Ward Cunningham.
Here is Sangers collection of "evidence".
http://blog.larrysanger.org/role-in-wikipedia/my-role-in-wik...
I find this paragraph most interesting.
Wikipedia’s first three press releases (2002, 2003, and 2004), including two that I had nothing to do with, all credited me as founder. It was not until later, in 2004 that Jimmy Wales began omitting mention of my involvement at the start of Wikipedia to the press, and he didn’t start denying that I am co-founder until 2005 or 2006, just when Wikipedia began to enter the public eye.
Wales claims that Sanger was simply an early employee and does not warrant founder status. Sanger claims that Wales is a suit whose primary early function in WP was to provide funding and that he himself (Sanger) not only originated the idea, but did all of the work, and is entitled to the label "co-founder".