Celibate Hero: Although when Panacea kisses him at the end of Asterix the Legionary, he falls for her just as hard as Obelix did. He also appreciates Cleopatra's nose ("Very pretty!"). It's implied that he has a thing for Bravura.
Ascended Extra: He was intruduced as a literal Running Gag character in Asterix and the Banquet, as a tiny little dog that keeps following Asterix and Obelix aroud without them noticing. Readers liked him so much that he returned in the next album as Obelix's dog, and would go on to play important parts in later stories, even starring in short books and comics of his own.
Authority Equals Asskicking: Averted. If there is an all-out threat that Asterix and Obelix can't manage alone, he takes the potion to fight like everybody else... but he always end dropped to the floor by his carriers.
On the other hand, he's shown to be either the second strongest person of the village after Obelix (whose Super Strength is active all the time), enough to deliver a Megaton Punchwithout magic potion.
Butt Monkey: Let's see, he has an overbearing wife, his carriers keep dropping him, and his village constantly fights amongst themselves with the slightest provocation.
On occasion he's been shown to be an acceptable musician - for example, in Asterix and the Normans - but a terrible, terrible singer.
Giftedly Bad: Despite his complete lack of talent, there are several characters over the course of the series who absolutely love his singing, and it has saved the day several times (such as by teaching the Normans the meaning of fear in Asterix and the Normans, or ending the Ganges valley drought in Asterix and the Magic Carpet).
Meaningful Name / Punny Name: Cacofonix, cacophony; Malacoustix, Mal + acoustics... less so in the original French (Assurances tous risques = Comprehensive insurance).
Nice Guy: He's said to be a very pleasant person as long as you don't let him sing.
Non-Action Guy: Unlike the other men of the village, he rarely takes part in fighting the Romans.
Though he does do so once, beating the crap out of the Normans with a horn.
Small Name, Big Ego: Despite being a terrible singer, he thinks he is a talented one. The almost universally negative reactions of everyone who hears him do nothing to dispel his illusion.
The blacksmith of the village.
Characterization Marches On: Fulliautomatix in Asterix the Gaul and Asterix and the Banquet looks and acts nothing like the character does in later books.
Drop the Hammer: Given that he's a blacksmith. But he seems to be all too willing to use it on Cacofonix and against the Roman soldiers in battle.
Jerkass: He's always starting fights with Unhygenix, hammering Cacofonix into the ground and mocking the advanced age of Geriatrix; he's basically the village bully.
Honor Before Reason: This is the reason why his fish isn't fresh; he could easily get fresh fish by just going fishing to the sea right next to the village, but he constantly insist on ordering it from Lutece, arguing it's of better quality back here.
Meaningful Name: In the British edition, he's Unhygienix. In the American, he's Epidemix.
Character Development: In the earliest albums, Caesar was little more than a villainous plot device that drove the Romans forward in their conquest of Europe; the original depiction doesnt even have the same design as the more well known version. Once he began to appear as an actual character rather than a generic Evil Emperor, he quickly became the dignified statesman he is for most of the series.
His name is Caesarion aka Ptolemy XV, and the reason Brutus takes on the Gauls' Village is Cleopatra sent the child to Asterix to keep him safe from Brutus.
Noble Demon: even though he is willing to use deception, tricks and manipulation, he will always keep his word when he makes a promise, and be grateful to his enemies when they help him. When he finds in "Asterix and Son" the Gauls protected his son with Cleopatra from a murderous, power-hungry Brutus intent on securing power in Rome, Caesar's more than amiable to repair the damage Brutus wreaked.
Third-Person Person: After explaining his plans to his lackeys: "Wow, he's amazing!" "Who?" "Well, you!" "Ah, him!"
The Brute: Well with a name like that... Later we see his tactical skill, it amounts to "Burn it to the ground".
Characterization Marches On: His appearance and general attitude has been largely unconsistant in the various cameos he made over the course of the series. It's not until Asterix and Son that he gets actually solid characterizations.
Foreshadowing: Just about every one of his appearances reminds us that he kills Caesar (though not in the series).
Caesar: (having gotten up to lead the others to the dining hall) You too, my son!
Brutus: (thinking) He's starting to annoy me with those classical allusions of his! One of these days I'm going to up and...
The Starscream: Asterix and Son reveals Brutus was after the "son" Asterix had because that was really Caesaerion, the son of Caesar and Cleopatra, and Brutus had tried to find AND kill the child to secure his ascention to the Roman throne. This story shows him out for once as a true Big Bad, and Caesar is aghast at this treachery.
Top-Heavy Guy: Like most of the centurions, has huge hairy arms and chest with normal-sized legs.
Better To Sink Than Be Sunk: On occasion, they will scuttle their own ship when Asterix and Obelix turn up; it saves them a few knocks and amounts to the same thing in the end.
Expy/Affectionate Parody: All of the pirates are expies of the characters from the Barbe Rouge (Redbeard) comics created by Jean-Michel Charlier and Victor Hubinon (and which, like Asterix itself, first appeared in the French comics periodical Pilote).
Origin Story: One album shows that the pirates were originally Roman slaves that were put to work on a Roman villa resort near Asterix village. After they talk the Gauls into letting them finish the project so the overseer will set them free, they are paid a wage they have earned, and are on their way, with the future pirate captain mentioning that they might invest in a ship.
Pirate Booty: Subverted; they always manage to cross paths with our heroes before they can steal enough to pay off their latest ship loan.
Reformed, But Rejected: In Asteric and the Cauldron, they give up piracy and open a restaurant instead. Unfortunately, Asterix and Obelix assume that they're the ones who stole the cauldron of coins and beat them up as per usual.
Face Death with Dignity: When she thinks Asterix wants to assassinate her, she holds a long speech about "showing the barbarians how a queen dies". Asterix eventually gets impatient and manages to throw a word in.
Hide Your Children: To protect her son with Caesar in "Asterix and Son," she sends him to the Gauls' Village. It leads for a Dramatic Reveal when Caesar finds out the truth of Brutus' treachery.
The best architect in Alexandria...which isn't saying much. Edifis' ramshackled buildings are the joke of everyone not living in them. In spite of this, he's given the job of constructing the palace for Caesar in three months, or be fed to the sacred crocodiles.