It is a darkish yellow metallic bipedal robot that looks similar in appearance to SpongeBob except for its lightbulb eyes, a metal bolt for its nose, a frowning mouth with glowing teeth, and a tail pipe behind it. One of the largest differences between SpongeBob and Robot SpongeBob is that Robot SpongeBob has a transparent glass container on its head that is filled with fluids, and it can hold SpongeBob's brain so that Plankton can get a Krabby Patty. Robot SpongeBob also has one arm that looks like a spatula and another that is a metal pincer.
"Goodbye, Krabby Patty?"
It appears to look like SpongeBob, just that it is put together with metal. 
It has the same general appearance as SpongeBob but he is made of metal and he has no porous holes on his body structure.
Role in series
"Welcome to the Chum Bucket"
Robot SpongeBob was a robot created by Plankton to force SpongeBob in to making a Krabby Patty and is confirmed as plan B. A few months after Plankton had failed to get win the card games he played with Mr. Krabs to get any amount of his money and/or secret Krabby Patty formula, he had finally won the card game (by cheating) and SpongeBob instead so that he should work at the Chum Bucket. SpongeBob did not have the proper ingredients to cook a Krabby Patty, but he was to be treated with compassion and understanding. Later, SpongeBob tricked Plankton by becoming less disciplined and calling him a bad name. Plankton took out SpongeBob's brain and put it into Robot SpongeBob and then, Plankton programmed it to make a Krabby Patty, but SpongeBob took control of the robot by saying through it to Plankton "Dee dee doodle dee dee doo. Response: Why don't you ask me later?". Then Plankton yelled at him to follow his order, but SpongeBob said "I don't wanna." and Robot SpongeBob lazily drank a can of oil while reading a comic book that had a comic strip of SpongeBob, Patrick and Squidward. Personality-wisely, it is shown to be sassy and trick Plankton by replying with a refusal response to follow his command to make him a Krabby Patty. The robot used that reaction, because it had SpongeBob's brain, which has his personality, thoughts and memories in it. Plankton just gave the brain a new body to maintain the brain which ultimately back fired which does not change that SpongeBob is taking advantage of Plankton. It is also shown he likes to drink oil and read comic books. Plankton becomes frustrated and puts the brain back into SpongeBob, himself.
"Goodbye, Krabby Patty?"
Robot SpongeBob is seen at the Krusty Krab at the kitchen. The real SpongeBob kicked it when he knowed that the frozen krabby patties are made with sand.
When Plankton leaves the Chum Bucket to retire, Mr. Krabs and Plankton follow him to a hotel. It is soon shown that Plankton was a robot the entire time, and the real one is at the Krusty Krab. However, Mr. Krabs and SpongeBob are revealed to be robots as well, and the real ones stop Plankton. With nothing left to do, the robots hang out and later explode.
Role in video games
"The SpongeBob SquarePants Movie video game"
He also appears in the PC version of The SpongeBob SquarePants Movie (video game) where Plankton must distract him to grab the jetpack without being crushed. Later, SpongeBob must avoid being seen by him in a maze while grabbing Krabby Patties.
It is called two other names: "RobotBob SpongeChefPants" and "RoboSponge".
Robot SpongeBob is also named "SpongeBot SquareShiftPants", which is not to be confused with SpongeBot SteelPants.
The premise of Robot SpongeBob in "Welcome to the Chum Bucket" is similar to The Simpsons' Treehouse of Horror II segment titled "If Only I Had a Brain," featuring Homer's nightmare. Homer, a lazy worker, is kidnapped by Mr. Burns and Smithers, who put his brain into a robot. The robot ends up being lazy and refusing to work, just like Homer.
Part of the control panel of Glove World in "Tunnel of Glove" looks just like the robot.
The robot is an obvious parody of Frankenstein's Monster, because in the book/movie Dr. Frankenstein puts corpse body parts to make the monster come to life, as seen here where SpongeBob's brain is transferred into the robot in "Welcome to the Chum Bucket."