A made up
person, used in reference to something else, to test if a
person is acting like he knows pop culture. The term was first used in Season 2, Episode 1 of Rick and Morty's “a Rickle in
time“
Beth: Honey, are you wearing your shirt backwards?
Jerry: What? Uh.. No, I just like my shirt on backwards. I'm not an idiot.
Rick:
Wow, that guy is the Redgren Grumbholdt of “Knowing-whats-going-on”
Morty & Summer: *laugh*
Rick: Huh? You like that? You like that Redgren Grumbholdt reference? Yeah, because I made him up. Think for yourselves, don’t be
sheep.