Strong Bad is the titular protagonist villain from Homestar Runner.com and Strong Bad's Cool Game for Attractive People (or SBCG4AP for short). He is mostly known for his email series (dubbed "Sbemails") where he responds to selected emails from fans and watchers.
Strong Bad started out in the children's book Homestar Runnner Enters the Strongest Man in the World Contest as the villain who tried to cheat his way to the top with his cohort The Cheat in a contest where the contenders held up stacks of large grapes. Although he managed to cause two of his fellow competitors to lose, The Cheat was defeated by Homestar who intervened and kicked The Cheat out of the way, although it cost him a chance at winning the contest. Strong Bad fared no better, getting crushed by his stack of grapes (earning him the brief nickname "Squished Bad" in the Internet toon adaptation of the book).
Since then, Strong Bad became the breakout character as a result of his Sbemails. With this and his inflated ego, Strong Bad often tries to create a total villain persona but often fails (particularly seen in the Sbemail "your edge").
Despite his tendency to falter and be more of a would-be villain, Strong Bad still has committed some rather villainous acts, even if they were met with less-than-spectacular results. He is particularly notable for the abuse he heaps upon his younger brother Strong Sad. Every Decemberween (the HR-verse equivalent of Christmas), he locks and boards Strong Sad in a tub. The concept of Strong Sad's death is relished by Strong Bad who once described receiving the latest Compy magazine as being like "Strong Sad's funeral" combined with birthdays and Decemberween. He also is fond of abusing his pet/associate/lackey The Cheat, typically by partaking in a game of "Kick The Cheat".
Among other things, he was also shown in the HR toon "Where My Hat is At?" attempting to murder Strong Sad in a pool via encasing him in cement and cursing his luck when Homestar inadvertently saved Strong Sad's life. He also once attempted to leave Marzipan and Homsar for dead after gluing them together but ultimately failed due to, as he put it, "Marzipan's resistance to death". In another Sbemail "your friends", he viciously assaulted many of the characters-smashing a gold record over Bubs' head, trying to get Marzipan to handle a sawblade and presumably tricking Homestar into dipping his head into a tank of lava-as per a fan's likeness for when Strong Bad beats people up. When irritated by fellow moviegoers during a showing during the sbemail "the movies", notably Homestar who kept having casual conversations with the film, Strong Bad attempted to kill everyone with a bazooka. This apparently happens on more than one occasions due to a pre-film advisory asking the audience to turn off their bazookas before the program.
Strong Bad is also fond of vandalism and thievery and will often resort to cheating to meet some end. This is often shown in parodic manner, such as the aptly-titled cartoon "Strong Bad is in Jail Cartoon" where he and The Cheat are arrested and locked up in a cardboard box jail for attempting to steal Bubs' fundraiser candy bars. In that particular cartoon, Strong Bad speaks of himself and The Cheat as having attempted the robbery in order to "pull off one last job before retirement".