Using "champion" as a verb [closed]
To champion something is to promote it.
Yes. To 'champion' in this context, means to be its defender and protector. In your example, John McCarthy being the champion of mathematical logic for AI means he argued in favor of that approach to achieving AI.
The previous two posters are right. Champion is first recorded as a verb in Shakespeare’s ‘Macbeth’, although with a different meaning from that in your example. It was first used figuratively in the sense ‘maintain the cause of, stand up for, uphold, support, back, defend, advocate’ in 1844. (Source: OED)