If they're real then why are they in a comic book?
Anastacio Somoza García:
The Shield meets with the President of Nicaragua and as per usual the artist did not bother to check what the President of Nicaragua actually looked like. (Pep Comics 006, 1940)
Clark Gable:
Boxer Kayo Ward stars in a movie ("Hot Lips and Hot Fists," a riff on 1933's "The Prizefighter and the Lady" starring real-life boxers Primo Carnera, Max Baer and Jack Dempsey) and the opening night crowd includes not only Clark Gable but
Edgar Bergen and Charlie McCarthy, all under their real names in a wild break from comics custom. (Pep Comics 008, 1940)
FDR:
Misc minor appearances:
Meets with the Shield (Pep Comics 006, 1940)
Shown blowing off a cabinet meeting to watch a boxing match (Pep Comics 007, 1940)
J Edgar Hoover:
He's never actually named but "the Chief of the FBI" and only person who knows the secret identity of Joe Higgins, aka the Shield, is clearly supposed to be J Edgar Hoover, and they do occasionally refer to him by his surname. (Pep Comics 001-004, 006-009, 1940)
Joe DiMaggio:
Famed baseball player Slugger Madaggio (or possibly MaDaggio) is murdered mid-game for failing to pay protection money. Two other players, Wheezy Seen and Cal Bubble, as well as a manager named Terrier are mentioned in the story but I simply do not know enough about baseball to know who they are references to, if anyone. Also, the lady in the above picture is Madaggio's wife and thus an oblique reference to actress Dorothy Arnold. (Pep Comics 007, 1940)
Joe Louis:
Boxer Kayo Ward is signed to fight Joe Louis for the heavyweight boxing championship, only Kayo is then kidnapped and replaced with a double by gamblers looking to fix the match, and when he manages to get free and fight for real the kidnapping has had enough of a negative effect on him that Louis sportingly calls the fight off rather than beat Ward to a pulp. They're supposed to reconvene in six months - will it happen in 1941? (Pep Comics 006-007, 1940)
Mata Hari:
Sent to Antwerp to extract a British general's daughter before the Nazi invasion, army hero Sergeant Boyle engages in some classic comedy of errors shtick as he accidentally brings back the wrong woman, only to find out that he has inadvertently captured the famed spy "Hatter Mary." (Pep Comics 008, 1940)
PT Barnum:
There are a lot of comic book circus mans who are some sort of version of PT Barnum but this guy, Barnham by name, really captures the spirit of the man with his exploitation of Paul Bunyan's ape-man friend. (National Comics 006, 1940)
the Seven Dwarfs:
The "Prince Buttonhead" feature in Pep Comics is from the school of one-page comic book humour strips that are best described as incoherent, with only the feeblest attempt at jokes or even a structured plot. The Five Dopes here (Block-Head, Lunk-Head, Stupid, Useless and Lame-Brain) are interesting for being so very on-model as a Seven Dwarfs parody. (Pep Comics 005, 1940)
Various Golden Age Comics Creators:
During Kayo Ward's rise to the top he fights a lot of also-rans, and compiling a splash panel of them dovetailed nicely with the grand comic book tradition of using your coworkers' names for mildly embarrassing purposes. In order (and focusing on MLJ credits because it's an illustrious group), we have:
Butch Blezard - Okay I have no idea who this guy is. Bad start.
"Canvas-Back" Shorten - Harry Shorten, co-creator of the Shield
"Chick" Biro - Charles Biro, creator of Steel Sterling
"Biff" Zoffer - Another mystery character
"Mush" Meskin - Mort Meskin, prolific MLJ illustrator
"Flash" Ashe - Edd Ashe, illustrator of the Wizard
"Nosedive" Novick - Irv Novick, co-creator of the Shield
"50 Second" Streeter - Lin Streeter, MLJ illustrator
"Slam" Sundell - Abner Sundell, MLJ editor
"Socker" Benson - probably not a reference, as he was a boxer faced by Ward in a prior issue. (Pep Comics 005, 1940)
Pep Comics was a real hotbed of this kind of thing in 1940, as seen in this ad for "Meskin's Matzhos" (Pep Comics 007, 1940)
Here's Charles Biro ditching work to catch a boxing match. (Pep Comics 007, 1940)
Handprints outside Grauman's Chinese Theatre, featuring "Biro W. Mouskin," "Sundell something (possibly M. Wood? as in Bob Wood, co-creator of Kayo Ward?) as well as "Mickey Looney" and "Joe E. Frown" (Mickey Rooney and Joe E. Brown, natch) (Pep Comics 008, 1940)
And finally, the movie that Kayo Ward stars in is a Sundell Production. (Pep Comics 008, 1940)
Unknown:
The specifics of Jimmie Fiddle here, with his entertainment column in the NY Reflection, and especially the detail of him rating things with orchids, ping my "this is a version of a real guy" sense quite hard, but I can't find a good thread to grab onto for a search. (Pep Comics 008, 1940)
EDIT: a list of New York periodicals of the 1930s turned up the NY Review as a possible original of the NY Reflection, but any further investigation is hampered by the popularity of the New York Review of Books. It's a dead end!