Isshiki Madarai is a major antagonist in the light novel Danganronpa/Zero. The Ultimate Bodyguard and designated guardian of the Hope's Peak Student Council, when he remains the only survivor after the student council is massacred, he takes matters into his own hands. He constantly antagonizes Ryoko Otonashi throughout the events of the book- even when killed multiple times by Mukuro Ikusaba, mysteriously managing to come back. It's eventually revealed that 'Isshiki Madarai' is actually not just one man, but also his seven identical siblings operating under his alias as well.
Despite their status as major antagonists in the book, the Madarai brothers inarguably display valor and dedication to innocents that were wronged, and their intentions to pursue and subdue a much greater threat inarguably displays a certain strand of heroism.
The Madarai brothers's appearance is thought to be based on the Naruto series character Orochimaru (seen on Villain's wiki), or at least bares a notable resemblance to the character. They are all incredibly tall, with wide shoulders and large hands- their eyes have a notable, exaggerated slant, and their tongues are very long and often hang out of their mouths.
As part of their bid to all masquerade as the same individual, they're also all shown- or suggested to be wearing- an identical outfit. This outfit is a simple black uniform with a white undershirt and black tie, matching black pants and shoes.
The Madarai brothers all share a very similar, collective personality- or at the least, any differences they have are not explored within the novel. As far as their values go, they are very dedicated to the Student Council. When the council is killed in The Tragedy of Hope's Peak Academy, the brothers are shaken- both out of enragement for failing their jobs, and equally out of humilitation for not being considered part enough of the Student Council to become involved or die alongside them.