Conversation so far:
What were some of Cosmo Kramer's pseudonyms?
He used the name H.E. Pennypacker
Which episode did Cosmo Kramer use this name in?
in The Puerto Rican Day“
What happened in the Seinfeld episode The Puerto Rican Day?
Kramer poses as a prospective buyer interested in an elegant apartment in order to use its bathroom
What other names does Cosmo Kramer use?
He also uses Dr. Martin van Nostrand
Which episode does Cosmo Kramer use this name in?
In the episode The Package
What is the main plot of The Package?
Kramer tries to get hold of Elaine's medical chart
What does Cosmo Kramer try to do with Elaine's medical chart?
to erase the negative comments her doctor has made

Question: Does he use any other names?
Self-contained rewrite: Does Cosmo Kramer use any other names?