Oil Man is one of Dr. Light's original Robot Masters (added in Mega Man Powered Up). He was originally made to research oil. However, one day (if one is playing as anyone but Oil Man) Dr. Wily
took all of Dr. Light's Robot Masters and reprogrammed Oil Man completely to do evil. If one is playing as Oil Man, Wily takes all the Robot Masters except Oil Man.
Oil Man is a very controversial character, as his original Japanese design looks just like a stereotypical blackface person used in the 30's. The localization team immediately saw this and he was changed in all other releases to be blue and yellow to avoid legal troubles.
Oil Man is a laid-back robot obsessed with oil and afraid of flames. His weakness, correspondingly, is Fire Storm, which also makes his splotches of oil burst into flame. His attacks are running around, jumping and shooting three packs of oil, and sliding on Oil Slider, which is his special attack for Mega Man to take. When Mega Man uses the Oil Slider, it is a dangerous weapon as it is tricky to not get hit while attacking. This is also Elec Man
's weakness attack, which makes sense as oil is an energy source much like electricity and Elec Man makes it very clear he dislikes using oil for energy at all.