Dr. Thomas Light, also rendered as Dr. Right (both from Dr.ライト Dr. Raito) in Japan and some localisations, is a major character of the Classic era and X era, debuting in the original Mega Man and either appearing or being referenced in the plot of most Classic and X games since. He is the creator of many of the series's central robot characters, including Mega Man, Roll, Rush, Proto Man and X.
Light is depicted in the games as a portly human scientist with a fluffy white beard and hair, usually seen wearing a labcoat. Though he rarely joins the action of the games, he appears as a father figure to his creations and assists them with new upgrades and advice when necessary.
In the Classic era, Dr. Light is typically depicted as a good-natured optimist, hoping to improve the world through his robot creations. He is also shown to be somewhat naive and gullible, however, sometimes setting the plot of a game in motion through his interactions with his rival and former classmate, Dr. Wily, whose jealousy of Dr. Light's achievements set him on the path to becoming a villain.
Mega Man
The original Mega Man begins as Dr. Light has just completed work on eight humanoid robots - Rock, Roll, Cut Man, Guts Man, Elec Man, Ice Man, Fire Man and Bomb Man - each designed to fulfil a purpose helpful to him and humanity as a whole. When Light's old friend, Dr. Wily, steals and reprograms six of these robots to use for world domination, Dr. Light converts Rock, initially designed as a lab assistant robot, into Mega Man and sends him on his way to stop Wily.
Dr. Light does not appear in most of the game, and as the game lacks any sort of intro, his name and crucial plot role are only explained in the manual. He does however appear in the ending, standing outside his lab and awaiting Mega Man's safe return, together with Roll.
Mega Man 2
In Mega Man 2, Dr. Light once again grants Rock his Mega Man upgrades to stop Dr. Wily, who has returned for revenge. Unlike the first game, he shows up in the game itself, appearing on the screen to notify Mega Man when he has completed a utility upgrade (Item-1, Item-2 and Item-3) and outfitting him with it.
X era
By the beginning of the X era, Dr. Light is implied to have passed from old age, leaving Dr. Cain to excavate the remains of his lab, where he finds Dr. Light's notes and also his final creation. The robot, dubbed X, has been given the ability to choose his own destiny and sealed away by Dr. Light so his AI could ensure he would not pose a threat to humanity.
Anticipating that X would one day be activated, Dr. Light has also left Light Capsules all over the world that contain a hologram of himself and upgrades for X. These holograms enable Light to appear long after his passing, either playing pre-recorded messages or functioning independently as an AI.
Official Data
Mega Man & Bass CD
Dr. Light's CD in Mega Man & Bass is located in Cold Man's stage, likely referencing the location of the first/mandatory Light Capsule in Mega Man X. It is encased in an ice block and requires the Wave Burner to obtain.