Portrayed by the late
Sandy Baron, Jack Klompus was
Morty and
Helen Seinfeld's nemesis on the TV sitcom
Seinfeld. The old man lived in a retirement housing development in
Florida where he spent most of his days bragging about his
astronaut pen that could write upside down. In his first appearance on the show ("
The Pen") Jack insisted that
Jerry take his beloved pen and then proceeded to tell everyone at the condo how his pen had been stolen by
Jerry. In the end
Jerry gave the pen back to Jack, however the old man continued to mention the pen to
Jerry in future appearances.
When Morty Seinfeld had a scheme to sell vintage raincoats ("The Raincoats") in New York, he called Jack and ordered him to use the spare key into the garage, retrieve the coats, and mail them express to him at Jerry's apartment. Instead Jack broke a window, cut his hand on the glass, packaged the coats in flimsy cardboard, and mailed them non-express (which led to the Seinfelds missing their charter flight to France). As a final blow, Jack left the broken window alone which led to someone breaking into the Seinfeld condo and walking off with everything inside.
Jack returned in "The Cadillac" when Jerry bought his father a new Cadillac. The old man assumed that because Jerry's act was so terrible Morty had embezzled condo treasury funds to buy the car. This accusation began a series of events that led to Morty's impeachment from the office of condo president. Following this episode the Seinfelds sold the Cadillac to Jack for $6,000.
After Jerry found out that his parents had sold the Cadillac he went to Florida to buy the car back from Jack. The old man demands $14,000 for the car and Jerry agrees. However before he can take possession of the car, Jack drives it into a swamp near Alligator Alley. After spending all his money on buying the car back from Jack and getting it repaired, Jerry found himself out of cash and credit and had to sleep in the car overnight.
Jack Klompus was a thorn in the Seinfelds' side for many years. The incident with the Cadillac was his last appearance in the series.