HP had their TC1100 back in 2004, and I loved it. It was a tablet XP computer with a separable keyboard and pen, and while not iPad/Surface levels of smoothness it was still amazing at the time. It wasn't MS hardware, but XP went to pretty great lengths at the time to make pen input a thing, so I guess that can count as part of their "pioneering" legacy.

Interestingly, here's a piece comparing the TC110 to the Surface Pro 3: https://www.pcworld.com/article/2363252/ten-years-after-hps-...