An aptonym is, as you'd expect, a name that is apt.
(Aptonyms are more often called aptronyms, but personally I think all the r does is make things more difficult).
An aptonym can be called a charactonym, too.
Aptonyms are found in fiction (Pilgrim's Progress has a character called Mr Valiant, who is, yes, brave; The Water Babies has an unbendingly stern character called Mrs Be-Done-By-As-You-Did; and Dickens uses aptonyms all over the place, for example his thrashing schoolmaster Wackford Squeers.
And then, much more recently, there are the Mr Men. Is Mr Happy totally miserable? No, he is of course a positive ray of sunshine. And good for him.
Aptonyms aren't just a matter for fiction, either. There's an idea called nominative determinism which says that if you're called John Butcher you're more likely to become a butcher than if you were called John Baker or John Fryer or John Sexton.
But is nominative determinism actually true? Well, in my area there's an estate agent called Profitt; one of England's chief judges until recently was called Judge Judge; Bob Champion was a successful jockey; and Thomas Crapper manufactured (though didn't invent) lavatories.
On the other hand, all the other estate agents in my area are called dull names like Doyle or Brown; most judges are not called Rule or Laws; and the current champion jockey is called McCoy.
But then I suppose that, as far as jockeys go, he is the real McCoy, isn't he.
Word To Think About Today: aptonym. In the form aptronym this word is said to have been coined by by the US newspaper columnist Franklin P. Adams.