Cory Radison is the Greendale Glee Club music director. He prefers to be called "Mr. Rad" for short. An upbeat, energetic, and enthusiastic person, he tries to convince the study group to once again fill in for the Glee Club when they are incapacitated. Although his first onscreen appearance is in "Regional Holiday Music", the character was mentioned to have been canonically part of a previous story briefly shown as a clip in the Season Two episode "Paradigms of Human Memory". Mr. Rad's first and so far only appearance is in the Season Three episode "Regional Holiday Music". He is portrayed by actor/comedian Taran Killam.
In the study group's second year at Greendale, they all volunteered to fill in for the Glee club when the student members died in a mysterious bus crash. When the Glee club for their third year at school becomes incapacitated, Mr. Rad tries to recruit the study group again to replace them. They were needed to perform at the Christmas Pageant but they all initially refused. However, Mr. Rad finds an ally in Abed who wants everyone to be together on Christmas. Eventually Abed manages to convince the rest of the study group one by one to participate by "infecting" them with "Glee".
Mr. Radison infects Abed with "Glee".
On the night of the Christmas Pageant, Mr. Rad reveals to Abed a darker side and his true intentions regarding the study group. What was meant to be a one shot performance was actually just the beginning. He wants them all to become permanent members, so they can make it to regionals and then continue past that onto a seemingly never ending series of competitions. Realizing he is unstable, Abed sets out to put an end to the pageant by enlisting Britta's help. She replaces his part as The Mouse King and goes onstage where she sings horrifically.
The pageant is only the beginning...
An incensed Mr. Rad stops the performance and starts yelling at Britta, which causes Jeff and Troy to jump to her defense. Dean Pelton tries to smooth things over by suggesting that Britta continue her awkward song, to which the audience enthusiastically agrees. Mr. Radison yells back a verbal tirade to the crowd that culminates with the admission that he was the one who caused last year's bus accident which killed the previous Glee Club members. Realizing he just confessed to murder, he distracts the audience and runs off stage.
Mr. Rad is a parody of Will Schuester, the Glee Club Director on the television show Glee. This is reflected in his constantly upbeat personality and his collection of sweaters (Mr. Schuester normally wears vests). Like Mr. Rad, Mr. Schuester's name is often shortened to "Mr. Schue." Mr Rad's asexuality also seems to be a reference to the sexually tolerant themes displayed in Glee.
“Well, this time I'm not going to kid you. It won't be easy. Your best won't be good enough, and ten times your best will be so bad, I will yell at you. But I promise, if we dig down...”— Mr. Radison
“Okay.”— Mr. Radison
“If we win regionals, then it's straight on to sectionals, and then a week later is semis, then semi-regionals, then regional semis, then national lower zone semis!”— Mr. Radison's evil plans for the study group
“NO, NO, NO, NO, NO, NO, NO! This show is supposed to be gleeful and bright and fun, and you can let me do that, OR THERE CAN BE ANOTHER BUS CRASH!”— Mr. Radison confesses