Irvine is Oscar the Grouch's niece, a baby Grouch. She stayed in Oscar's trash can while he was away, in episode 2606 of Sesame Street. She has also made many other appearances on the show, up through Season 30. She has a tendency to scream & cry very often. Her parents aren't seen in the series.
In Episode 2402, Maria watches Irvine while she's taking her nap for Oscar, who had to go the Grouch supermarket. Unfortunately for Maria, Count von Count wakes Irvine up w/ his counting, & Maria can't get Irvine back to sleep. Biff & Sully (mainly Biff) tell her the story of Cinderella, but that doesn't work either. The Two-Headed Monster plays her a violin lullaby, but that doesn't work & they start crying too. Then, when Oscar returns, he tells Maria, who gives up, there's only 1 way to get a Grouch baby to go back to sleep. He starts yet another argument with Grundgetta & Irvine falls asleep in a matter of seconds. Oscar says Grouch babies love to fall asleep to the sound of a good loud argument.
In a 1998 episode, Irvine insists that she be allowed to take a bath, much to the concern of Oscar. After allowing Irvine to take a bath, Oscar remarks, "She may be clean, but she's still ugly."