Dr. Light is a scientist of robotics, and created Mega Man and Mega Man X both. He is a kind man who cares deeply about his creations. He is also the sworn enemy of the nefarious Dr. Wily and has had a long time struggle with him.
Dr. Light joined the Robot Institute of Technology in 19XX and met Dr. Wily. They were partners, but Dr. Wily was very envious of Light due to the fact he was better and got a Nobel Prize in robotics, which was a toss up between Light and Wily. After they graduated, Light never saw Wily until years after.
Before that, though, Dr. Light made a new robot with A.I. heavily independent called Proto Man. The problem was Proto Man had too much freedom and sense of independence, leaving Dr. Light. Using his knowledge of this, Dr. Light made two more robots, Mega and Roll, to be his assistants, but this time they had no independence like Proto Man. They obeyed and helped Dr. Light all the time. Dr. Light later made Guts Man, Cut Man, Bomb Man, Ice Man, Fire Man and Elec Man, all for some particular reason.
In the year 200X, Dr. Wily was upset with Dr. Light still, so to make it even, Dr. Wily stole all of Dr. Light's new robots and reprogrammed them to do evil. Although Mega had no independence, he knew when justice was to be given, and asked to be a fighting robot instead of an assistant so he could save his brothers and stop Dr. Wily before any huge damage is dealt. However, he was not to kill him because the first law of Robotics says that robots are not permitted to kill. After he was changed, Dr. Light officially called him Mega Man and gave the ability to change weapons.
After Dr. Wily was defeated, Dr. Light still had to deal with him for years, having some projects copied or stolen. However, Dr. Light did start a new project: Mega Man X. This was a new kind of robot called a Reploid, a free-thinking and independent robot. Due to the fact he was not sure how people would think of it, Dr. Light sealed Mega Man X for years, and was found by Dr. Cain after Light passed away. This new type became popular, and the Mega Man X series is filled with these. Before he died, Light made special hidden capsules across the planet for his future robot to see and use for weaponry, which appear in all Mega Man X games.