1. Katherine Pulaski
I may be in the minority for saying this, but I wish that Dr. Pulaski (Diana Muldaur) had stayed the Chief Medical Officer of the Enterprise-D after her appearances in the second season. I know that many people prefer Beverly Crusher, but Pulaski serves an important role in Season 2 of Star Trek: The Next Generation that is missing in every other season of that show.
Beyond being exceptionally good at her job, Dr. Pulaski is not in perfect lockstep with every Starfleet attitude. Some may find this derivative of TOS’s Dr. McCoy, but I find a character like that almost more necessary on TNG, where an air of uncritical moral righteousness can often permeate from members of the crew, especially Captain Picard.
Of course, we have other characters who will push back a little on these attitudes—such as Ro Laren, Worf, or Q—but Pulaski’s clear position of largely approving of the Federation and Starfleet makes it so that her critiques cannot be explained away as either being an outsider (Ro and Worf) or being an outright antagonist (Q).
Pulaski represents ideals that are quintessentially Star Trek. She has views and opinions, and she presents them honestly. Critically, though she is also tolerant of those who disagree with her and open to having her mind changed.
Overall, I find Dr. Pulaski to be a fun character to watch, whose contradictions and disagreements with the likes of Picard and Data helped to ground those characters into something other than untouchably perfect paragons. She was not rude, but she also wasn’t mealy-mouthed. Pulaski spoke her mind and was skeptical without being stubborn.
While the bumpy production drama of early TNG is the likely culprit for Diana Muldaur’s brief tenure on the show, I sincerely believe that Dr. Pulaski is the most underrated character in all of Star Trek. I wish that she could have stayed for the rest of the series. If nothing else, I personally prefer her to Dr. Crusher, but that’s just me.
Conclusion
There are many good characters in Star Trek, and the sheer number alone means that many will be forgotten or dismissed in favor of the big names. This was a very difficult list to construct, as I found myself constantly thinking of other characters whom I felt deserved more love than they seemed to get.
All along, I knew that Dr. Pulaski would be at the top for me, but the other characters were in more flux. As I said, shows like Voyager and Enterprise are replete with underrated characters. If you’re interested in who some overrated characters might be, though, I encourage you to check out what Anthony Cooper wrote on that subject.