Question: who played janet's sister on three's company

title: List of Three's Company characters
text: Jack is known for being a klutz . Much of the character 's humor is derived from slapstick comedy . He is extremely clumsy and accident - prone , and is well known for his comic pratfalls . Jack is somewhat of a ladies ' man and a playboy , but is also kind , loyal - and protective of his roommates , family , and friends . Despite having been a boxer in the Navy , he often cowered and allowed other men to bully him ( mainly because of their larger size ) . Also , Jack is plagued by a fear of flying , as revealed in the episodes `` Up in the Air '' and `` Cupid Works Overtime . '' Jack has his own bedroom , while Janet and Chrissy share a second bedroom . A poster of The Beatles as they appeared late in their career can be seen hanging on the wall above Jack 's bed . ( The Beatles poster actually belonged to Ritter , an avid Beatles fan , and he lent it to the producers to hang on Jack 's bedroom wall . )