Gamma

Gamma (ガンマ) is a giant peacemaker robot constructed by Dr. Light and Dr. Wily. During Gamma's construction, Dr. Wily feigned peacefulness, gaining Dr. Light's trust and assistance long enough to complete the big robot. Dr. Wily's true intentions were to use the enormous creation as a weapon, furthering his evil plans for world domination.

Gamma is the final boss from Mega Man 3. In its first form, a small blue head shoots from the mouth. The head is weak to Hard Knuckle. After destroying the small head, Wily completes Gamma's head and controls him, attacking with shoots and punches. Gamma's second part is very vulnerable to Top Spin, and can be defeated in seconds by using it rapidly in the part with Wily.

Other media
In the cartoon Captain N: The Game Master, Gamma is a giant yellow ball robot with blue details. He has a large smile and the peace symbol drawn on him, as Gamma was originally created for peace. It has also a cockpit in the top of his head, where Dr. Wily controls it.

In the manga Rockman Gigamix, Gamma appeared in the story "Asteroid Blues", which is based on the events of Mega Man 3. Mega Man fights against him in space. Gamma also had a brief appearance in the beginning of the story "Metal Heart" from Rockman Megamix.

Trivia

 * Gamma (Γ) is the third letter of the Greek alphabet. He is the first in the Mega Man franchise to have a Greek letter for a name although three other characters, Epsilon (Ε), Sigma (Σ) and Omega (Ω), share the same naming convention.
 * Sigma's final forms in Mega Man X5 and Mega Man X7 are similar to Gamma.
 * In Mega Man X4 during the cutscene of a duel that place between Sigma and Zero, Sigma mentions a Maverick Hunter named Gamma that was destroyed along with his troops by Zero (The English version of that scene may sound like "Garma", however it was still Gamma just with a different pronunciation). However, the namesakes were most likely coincidental and has no connection whatsoever to the classic-era Gamma and Dr. Cain most likely chose the Greek alphabet as a naming convention.
 * Again, this robot also appears a bit like Guts Man