In which Mega Man game does Dr. Wily first pilot a giant robotic suit?

Dr. Wily first pilots a giant robotic suit in Mega Man 1. The original game concludes with Mega Man infiltrating Wily's robot manufacturing facility, where Wily operates the first Wily Machine.

This machine is known as Wily Machine No. 1 and serves as the final boss of the original game. Wily controls it from inside using his UFO, making it the earliest example of his recurring piloted combat machines.

Mega Man 2 also features a Wily Machine, but it is a later model rather than the first appearance of the concept. Subsequent classic-series games repeatedly return to variations of Wily's machines, capsules, and other large-scale weapons.

The distinction is between Wily creating or controlling giant robots generally and personally piloting a giant robotic suit. For the latter, the first instance occurs at the end of the 1987 Mega Man game, before the series introduced Wily's fortress in the form commonly associated with later entries.