R.O.B. & Professor Hector

R.O.B., (short for "Robotic Operating Buddy"), was an accessory that was packaged and made to operate with the NES to market it as a toy (increasing sales, due to the video game crash before). It worked with two games, Stack Up and Gyromite, both treating R.O.B. as a 2nd player that would react with different flashing commands from the TV. It has made various cameos throughout many Nintendo games.

Kirby's Dreamland 3
In Kirby's Dreamland 3, there was a level in Sand Canyon that featured collecting various parts of R.O.B. in order to collect the Heart Star of the level. After collecting all the parts in the level (which is 3-6), Kirby would be rewarded by the main character in Stack Up and Gyromite, Professor Hector. This was one of the first cameos R.O.B. would make in another game.

Super Smash Bros. Brawl
In |Brawl Brawl, R.O.B. is a playable character that can be unlocked by either playing 160 Brawls, getting 250 different trophies, or recruiting him in the Subspace Emissary, then defeating him in a brawl (with the exception of the last way). It has projectiles such as lasers and gyros that it may use to attack from a distance, and it can do various spinning attacks. Because of its great match-ups, high priority, and good projectiles, it is 12th in the current tier-list.

R.O.B. is also an enemy in the Subspace Emissary, coming in 3 types: Sentry, Blaster, and Launcher. Sentries are the closest resemilance to the default R.O.B. color in brawl. They are tan with red arms and will attack by hitting your character. Blasters are the same color as R.O.B. in his 'American-version' color pallete. They are able to hover all around, and attack by shooting blue lasers. Lastly, R.O.B. Launchers are camoflauge green and remain stationary. They will attack by launching (hence the name) slow-moving heat-seeking missiles that explode upon contact with a solid object.