To compare two people to Frick and Frack implies they have a close relation and are very similar in many ways. "Stalin
go together like Frick and Frack."
The origin comes from a pair of Swiss
ice skaters who performed comedy stunts for the Ice Follies
in the late '30s. Each dressed in matching lederhosen
and wowed the crowds with a trick they called the "cantilever
spread-eagle". Frick's real name was Werner Groebli and Frack's was Hans Mauche.
For a time Frick and Frack were so popular they were the highest paid professional ice skaters in the world. Their popularity and association was so well known that they became synonymous
with interpersonal symmetry, much like how people might say "they go together like Gilbert and Sullivan