Brutus and Nero are both ferocious, mean, and harmful. They show nothing but loyalty to Madame Medusa until the end. However, to Mr. Snoops, they show neither loyalty nor respect to him. They heartily dislike him, no matter how many times Mr. Snoops tries to make friends with them. It is clear that they can understand every word that is said around them.
Brutus and Nero first appear watching Penny, an orphaned little girl, and making sure she doesn't escape, all while knowing she is not intimidated by them. They later have to find Penny because of Medusa's incompetent assistant, Mr. Snoops.
When the crocodiles find Penny, Brutus grabs Penny by the straps of her dress while Nero takes her Teddy Bear. Penny bravely chides the crocodiles for ruining her escape and threatens Nero for if he gets her Teddy Bear wet. When they return to the river boat, Brutus carries Penny upside down by her bloomers. Mr. Snoops taunts Penny for her failed escape. Then Penny orders Brutus to put her down. Brutus smugly drops her to the floor where she lands on her head. Penny calls him a "freaky little dragon" for that.
Brutus and Nero are congratulated by Medusa while she confronts Mr. Snoops. Later, Brutus and Nero try to eat Bernard and Bianca, two rescuing mice, who are going to rescue the kidnapped Penny. However, when Medusa hears them playing the organ, where the mice were hiding in, she stops them from making a lot of racket. Medusa sees the mice and she, Mr. Snoops, Brutus and Nero try to kill them both, but they all fail.
Brutus and Nero, after Penny is forced to get the diamond for Medusa, take Penny back to Medusa's home. Again, Brutus holds her upside down by her bloomers, prompting her to demand he put her down. This time, he ignores her, swings away from the cave and continues carrying her while Medusa and an arguing Snoops follow.
The animals help Penny by attacking Medusa and outsmarting her on every move. Brutus and Nero are tricked into going after Bernard and Bianca, and they become trapped in the elevator by the mice. Brutus and Nero are freed after the house falls apart. Medusa then hits them both with a rope in the final chase, presumably to make them go faster. However, they all land onto a pole that used to be part of Medusa's home. Realizing that their mistress has no real respect for them, Brutus and Nero attempt to eat Medusa in revenge for her abuse towards them in the end.
Despite not appearing in the game, Brutus and Nero have a cameo in the Graphic Novel as random crocodiles in Bog Easy, which make sense given that Madame Medusa's boat already appeared in the same place in Epic Mickey.
They are likely based on the bloodhounds Tyrant and Torment, from Miss Bianca.
Brutus and Nero are crocodiles. They are called "crocs" by Miss Bianca during her, Bernard and Penny's escape plan. It is also noted that crocodiles show both their top and bottom teeth and have V-shaped snouts, whereas alligators only show their top teeth and have U-shaped snouts.
The idea of Brutus and Nero understanding everything that is said to them makes sense, since crocs are surprisingly intelligent.
Brutus and Nero may have also inspired the pets of several other Disney villains:
Brutus perhaps was named after the adopted son of Julius Caesar, who in the end betrayed him; or either with another Brutus who assassinated the last King of Rome, Tarquinius, and started the Roman Republic, which was however later turned into an empire; and Nero was named after a tyrannical Roman Emperor named Emperor Nero.
An unnamed crocodile with a similar design to Brutus and Nero appears as a minor villain in Jungle Cubs.
The scene of Brutus and Nero attacking Bernard and Miss Bianca is parodied in the non-Disney animated film The Swan Princess, where two alligators attack Jean-Bob the frog.