Not Merlin, but I don’t know his first name. Take 2 DQs as I didn’t really know your previous one, just guessed, and I didn’t get the correct first name.
Marvin Miller.
DQ
Is this character one primarily of the detective/police/crime genre, as opposed to other genres?
IQ
Have you scared American parents senseless since the 90’s?
Did you break the reserve clause, and bring free agency to major league baseball players?
This was Marvin Miller, but I won’t take a DQ because someone else asked about him
Did you say appear as yourself in"Annie Hall" and tell a pedantic twerp that he’d completely misinterpreted your theories?
THis was Marshall “The medium is the message” McLuhan
Did you star in “The High and the Mighty” under a more macho name?
THis is Marion Morrison, who adopted the stage name John Wayne
Did you keep the beat for the Jimi Hendrix Experience?
THis is drummer Mitch Mitchell
Were you the Ugly Duckling niece at 1313 Mockingbird Lane?
This was Marilyn Munster, on the sitcom “The Munsters”
===========
DQ1: Is your creator American?
DQ2: Have you ever been a character in a movie?
DQ3: Is your creator male?
DQ4: Are you considered a “good guy”?
Still unanswered, I believe.
Are you the only person to play professional baseball in his 20’s, 30’s, 40’s, 50’s, 60’s, and 70’s?
You originally asked the question in post #21, and Dead Cat later said that each IQ “after post #20” received a DQ, so that includes the identity of “one of LA’s finest”. On that note:

My IQ’s:
Did Jerry Seinfeld attempt to exploit your lip-reading ability?
Are you a baseball pitcher and pitching coach overshadowed by your brother, who’s been much more successful on the mound?
The respective answers I had in mind were Marlee Matlin and Greg’s brother, Mike Maddux.
My DQ"s:
-
Are you in a work (or several works) of British literature?
-
Do you die in your character arc?
IQ:
Were you a rodeo trick rider who took your stage name from a state with which you were associated?
Are your first and last names both the same as your rank?
I’m going to guess this is something Mrs Max Moseley said during the recent shenanigans, and I’m not him.
No, it’s Mr. Micawber from David Copperfield. DQ for me!
Are you American?

You originally asked the question in post #21, and Dead Cat later said that each IQ “after post #20” received a DQ, so that includes the identity of “one of LA’s finest”.
Oops, sorry, I overlooked that. Martin Milner was a star of Adam-12, about the LAPD.
I’ll wait to ask my DQ until I see how the other DQs are answered.
People, people! The OP answered way back in post #12 that he was a fictional character, so a lot of these questions are moot.
Edit: my question’s already been answered, so I’ll think of another.

People, people! The OP answered way back in post #12 that he was a fictional character, so a lot of these questions are moot.
Irrelevant, because then, the purpose of asking those questions is to stump the OP so you can ask a DQ, not necessarily to actually try to find the answer.
Ah, got it. Seems underhanded. But I don’t say that as a value judgment. More respectfully.
OK, now that I’m clear on the rules:
Are you a bass player/keyboardist for a (still semi-)popular band?
My four, in order:
The oboist is Mitch Miller, Martin Mull recorded “Dueling Tubas”, Mary Martin went from stripping to a nun, and Max Miller is the music hall performer.
My DQs:
-
Are you a character that started in periodical fiction?
-
Have you ever been adapted for television?
-
Did you originate in the English language?
-
Have you appeared in any original work in the last ten years?
Were you ever the IOC boss?
Did you write a best-seller with Irving Wallace’s son?
Do you go by the name “Mr. Speaker”?
Sorry for the delay, I’m on UK time!

Marvin Miller.
DQ
Is this character one primarily of the detective/police/crime genre, as opposed to other genres?
No.

IQ
Have you scared American parents senseless since the 90’s?
Not Marilyn Manson.

DQ1: Is your creator American?
DQ2: Have you ever been a character in a movie?DQ3: Is your creator male?
DQ4: Are you considered a “good guy”?
Yes, yes, yes, and probably yes, although this character also has some bad points.

Are you the only person to play professional baseball in his 20’s, 30’s, 40’s, 50’s, 60’s, and 70’s?
American sports, so DQ.

My DQ"s:
Are you in a work (or several works) of British literature?
Do you die in your character arc?
IQ:
Were you a rodeo trick rider who took your stage name from a state with which you were associated?
No, no, and I’m going to take a complete guess with Mississippi Mike, but I strongly suspect another DQ will be in order :).
Are your first and last names both the same as your rank?
I’m not Major Major Major Major.
No, it’s Mr. Micawber from David Copperfield. DQ for me!
Are you American?
Fair enough - yes, I’m American.

Are you a bass player/keyboardist for a (still semi-)popular band?
I don’t know who you mean, take a DQ.
Are you a character that started in periodical fiction?
Have you ever been adapted for television?
Did you originate in the English language?
Have you appeared in any original work in the last ten years?
No, no, yes, and no, AFAIK. Also, I’m not Michael Martin, but you can take two more DQs.
Summary:
Fictional
Character in literature
Male
20th century
Not crime genre
American creator
Been in a movie
Male creator
“Good guy”
Not British literature
Not dead
Not in periodical fiction
Not adapted for TV
Originated in English
Not appeared in the last ten years
The pro baseball player was Minnie Minoso.
DQ: Was your first appearance after World War II?
IQ: Did you change your name and become one of the biggest Hollywood stars ever?

The pro baseball player was Minnie Minoso.
DQ: Was your first appearance after World War II?
Yes.

IQ: Did you change your name and become one of the biggest Hollywood stars ever?
Marion Morrison (aka John Wayne) and Marilyn Monroe (aka Norma Jean) have already been mentioned - perhaps you could be more specific?