In the episode "The First Day of Summer", it's actually revealed he really likes everyone in LazyTown, including Sportacus, and has nothing to do if they're all gone. He also sometimes appears to be extremely friendly, empathetic and compassionate on terms with the LazyTown residents at times. Towards other LazyTowners, he's very argumentative and grouchy, though in his disguises, he's sociable, charming and funny, all in his bid to make a slothful life seem like an attractive alternative to Sportacus's example. Despite all of his silliness, exuberance and antics, he also exhibits remarkable engineering skills and scheming skills. He's remarkably aloof and clown-like in his voice and movements in a incredibly cartoonish, energetic and exaggerated way, he also tends to be rather jocular, flamboyant and over-the-top, as well as throwing child-like tantrums at the drop of a hat. Generally, Robbie is extremely bitter, obnoxious and vituperative towards Sportacus in particular, desiring to humiliate him a lot and have him very ostracized just so that he'll leave LazyTown forever.
He has a strange and contrasting attitude towards everyone in town, but he deeply despises Sportacus. He also has very poor social skills when he isn't scheming. Though, he's also often a very, very childish buffoon. Despite his laziness and desire to inspire laziness in others, Robbie himself is quite slim and (when he has to be) hardworking, incredibly strong (as seen when he lifts a massive cannonball twice the size of his head in Robbie's Dream Team), as well as intelligent and a genius (as he said to himself in "Robbie's Greatest Misses"). Nonetheless, he's a true mastermind inventing all manner of devices, and his disguises actually fooling people. Despite his flaws, Robbie shows certain degrees of lots of brilliance, though his presence in a children's show restricts his success and cruelty as a supervillain. Robbie is shown to have an awful diet, being a lover of sugary treats that he eats throughout the show, such as ice cream and blue frosted cake (which he then tops with whipped cream), and even ate a cake containing sand once. Normally, he's an extremely lazy and greedy person he's apparently very proud of these traits, and works hard at keeping his status as a supervillain. Robbie Rotten is a very immature, conniving, egocentric and manipulative trickster with many vices. He’s also shown to be the tallest character in the show, even more so than Sportacus.
He usually wears a two-piece suit of maroon and purple with gold pinstripes, formal shoes, a navy blue shirt with cuffs and cuff links. Despite his very unhealthy diet and habits, Robbie is surprisingly tall and slim, has fair skin, greenish-gray eyes and black hair.