The Beano extends this to relatives of the characters so named—The teacher of the Bash Street Kids is called "Teacher" and his wife is "Mrs. Teacher". Similarly, one strip features the headmaster's brother—Mr. Headsbrother. The comic once claimed in response to a reader's letter that Dennis the Menace's father was actually named "Dennis' Dad" at birth, and knew he had found his future wife when he met a girl called Dennis' Mum.
In Beetle Bailey, most unlisted men refer to Sarge as simply "Sarge", and not his full name, Sergeant Orville Snorkle. (He's never expressed dislike of his name, but still...)
The World's Greatest scientist in Catstronauts is only ever called "The World's Greatest Scientist".
Fall Out Toy Works has the Toymaker. As for his real name, the synopsis for the second issue had it as Jasper, one of the data files Mr. Moth brings up in the fourth issue has his name as "Chris Toymakeras". The final page of the final issue reveals his name is actually Alistair and brings up the possibility of his last name actually being Toymaker.
The Sage and The Minstrel from Groo the Wanderer. They have never had any other names and Word of God says they never will (and many speculate they ARE their names, and are possibly magical spirits of some sort). Sage's dog, however, got a name after much fan needling ("Mulch," based on a running gag from the letter's page).
From Nextwave, the Captain. According to Aaron Stack, if the Captain ever had a real name, he's forgotten it. (He is not actually the captain of anything.) It is later revealed he'd tried everything, including Captain ☠☠☠☠ ('☠☠☠☠' being an unspecified but extremely rude word), but had been sued and/or beaten up by Captain America until he settled on The Captain. And he still had to pay "some Marine-looking melon-farmer" royalties.
The book's theme song, when describing each character's notable trait, includes the words "The Captain! / ...HIS NAME IS THE CAPTAIN!" (while describing, for instance, that one other character "Is going to microwave your ass").
Planetary: The Drummer. First name the, second name Drummer.
Richard Dragon and Bronze Tiger's martial arts instructor, or sensei, is has been known only as "O-sensei" since the 70s. Whether the O stands for part of his actual name or is something someone tacked on to the front of sensei he took a liking to has been left unanswered.
In Shazam comics, the Marvel family gets their powers from a wizard named Shazam, and (except for Freddy) activate and deactivate their powers by saying his name. This happens anytime they say his name, even if they don't want to transform. As a result, they normally just refer to him as "the Wizard", and his name as "the Magic Word". In the New 52 reimagining, this was altered so intent matters: if they say his name with intent to transform, then they'll change, but if they don't intend to transform, it has no effect.
Most of the Smurfs don't have names, but refer to one another by their most prominent personality trait: Brainy Smurf, Handy Smurf, Grouchy Smurf, etc. This gets taken to the extreme in the live-action movie with the mention of Passive-Aggressive Smurf.
One cartoon featured a Smurf who had no name at all, seeing as he didn't have any talent he knew of that he could name himself after - he simply called himself "Nobody Smurf". When he eventually became the hero by defeating an evil goblin because he had no name or talent (the goblin was a trickster who inflicted Baleful Polymorphs on victims depending on their personalities) they decided to call him "Somebody Smurf".
Tintin's constant companion is known only as Captain Haddock until the second last comic in the series, and Tintin rarely refers to him by anything else other than simply Captain. In said comic, the Captain's first name is revealed to be Archibald.
In the Transformers comic series "The War Within: The Dark Ages," a character is introduced who is only ever referred to as "the Fallen," as his name was taken away from him by his fellow Transformers after he betrayed Primus and sided with Unicron. His name used to be Megatronus Prime, and he was one of the original Thirteen before becoming The Fallen.
The Beast from Transmetropolitan. He presumably has a name but it's never shown on-screen, and claims everyone just calls him "The Beast" — including his own kids. Also Spider's old boss who is never shown in person whom he only refers to as "The Whorehopper".
Used in a significant manner in V for Vendetta. The Head is only referred to by title for the bulk of the story... but people start referring to him by his actual name once his Villainous Breakdown causes a loss of faith in him.
In W.I.T.C.H., everyone refers to the Oracle as Oracle. Which leads to trouble while asking who was elected Oracle. ("What's the Oracle's name?" "You just said it"). A fallen Oracle is even unable to remember his name.