Osaka-ben (Osaka dialect) used to be the stereotypical villain accent until Osaka comedians performing with their accent became popular in the nineties. These days Osaka-ben is generally used to indicate a fun loving, impatient, loud, boisterous personality. (See also The Idiot from Osaka.) Osaka-ben speaking comedians are common in Real Life and in anime, and the Boke and Tsukkomi Routine, or owarai, has its roots there. Recall, for instance, the scene in Azumanga Daioh where Tomo learns that the new transfer student is going to be from Osaka, and wonders if she'll have an incredible tsukkomi. The comedy routine consists of the boke [funny guy], who generally says stupid things, and the tsukkomi [straight man], who corrects the boke though slapstick/physical devices, such as a rap on the head. Think Blackadder and Baldrick and you get the idea.
A few quick tips for catching a character speaking Kansai-ben:
Oddly, Kansai is sometimes so strongly associated with certain personality traits that characters with those traits are given the accent even when they are not actually from the Kansai region, and would have no legitimate reason to have learned the accent. This includes foreigners/Westerners, who would more likely have learned "formal" Japanese, but are considered to have the brash, outspoken Osakan personality. Similarly, the association between Kansai-ben and a specific character archetype is so strong, shows set in the region (but where the setting is not immediately relevant to the plot) may go out of their way to avoid giving the characters this dialect, even if it would technically be appropriate. (See The Melancholy of Haruhi Suzumiya for a show set in the heart of Kansai (in the suburbs of Kobe, to be precise), but where everyone speaks Standard Japanese.)
Depending on the country, preserving these dialects through translations and dubs can be tricky.
(An Accent Adaptation is when a translator substitutes dialect in their own language for one in the original work's language, making for a Woolseyism in some cases and Adaptation Decay in others, especially when the translated dialect doesn't have an equivalent in the original work.)
Regional accents used to adapt Kansai-ben in European languages.
Swedish reviewers of SDK say:
"Kommer ihåg att en av karaktärerna, Benitora, i Samurai Deeper Kyo pratar göteborgska. Lite underligt men på något sätt så tycker jag att det är charmigt och anledningen gissar jag är för att peka ut det faktum att han egentligen pratar någon japansk dialekt i originalversionen."
"Men en annan jag tycker om är ju den röda tigern, hans göteborgska är ju Gööörskön!! ;)"