Microsoft invented XMLHTTP, an ActiveX object, not XMLHttpRequest, that is similar but not proprietary, and a part of Ajax. And Ajax is a term invented by Garrett - and not Microsoft - that includes several W3C formats.
Like the GP that bit about AJAX was just all wrong. Garrett is so astonishingly irrelevant in all of this, as is the AJAX me-too title. Google was very important, but only insofar as they legitimized the technique and made a lot of people realize that this crazy web thing was a lot more powerful than people often thought. And it wasn't gmail -- it was Google Suggests. That was an atomic bomb on webapps that proved that highly dynamic pages were possible and preferable.
Me - using XmlHttp(Request) since 2001.