Jenna Maroney is a character on 30 Rock, played by Jane Krakowski.
Jenna was the star of The Girlie Show, a sketch comedy series created by her friend Liz Lemon. Jenna's star billing was reduced drastically when Jack Donaghy brought in Tracy Jordan, a popular and unpredictable actor.
Moreover, Jack decided that Tracy is more a priority than Jenna so he orders the show's title change to TGS with Tracy Jordan.
The move left Jenna furious because not only was she left out of the loop, but upset that Liz Lemon gave in to Jack's demands.
She finds herself at the mercy of Tracy's mentally unstable antics, the writing staff's constant pranks, and Jack's constant avoidance of her.