What should I call someone who has a tendency towards monologues?
Solution 1:
soliloquist ?
It is cited in the Merriam-Webster's.
As for the fact that it would apply to dramatic art, that's perfectly true. That's actually the same for "monologue" the origin of which lies also in dramatic art.
Monologue comes from the Greek μονόλογο - μονός (alone) - λόγος (discourse) and is a common rhetoric style in Greek dramatic art.
Soliloquy comes from Late Latin soliloquium, (solus alone + loqui to speak) and is also common in this specifically Latin genre: satire.
There is however, a slight difference between these two words.
You can engage in a monologue in front of somebody who will just stay silent or nod. Greek plays monologues often addressed the audience. But basically you speak aloud because you intend to be listened to.
To soliloquise is instead, just to think aloud in front of nobody. In the case of a play, it's just a dramatic device so that the audience can share the character's thoughts (numerous examples in William Shakespeare's plays). In real life however, it is obviously unnecessary and can therefore sometimes be considered inane.
As a conclusion if your character makes a long speech in front of some auditor, then he could be called a "monologist" whereas if he is just thinking aloud with only his own ears around, then he should be called a "soliloquist".
One last word.
I initially thought that soliloquy was also a medical term. I could find no evidence for this. At least in English.
It is in French though: ("En médecine, on parle de soliloquie lorsqu'un individu ayant des troubles de la personnalité et du comportement se parle à lui-même").
Solution 2:
I assume that “a narcissist” wasn't what you were looking for.
I would argue against “monologist” because my first instinct was to read that as somebody who studies monology (whatever that might be). “Monologue” and “soliloquy” are certainly distinct things in drama, but there are plenty of technical terms used in a fuzzy way by the general public. I think “soliloquist” is fine, even if it might be a neologism.
Solution 3:
- loquacious
- garrulous
- logorrheic
- discursive
- uninterruptible
- blowhard
- deaf
Though not directly an answer to you question (these are mostly adjectives), they still imply what you want.
Solution 4:
monologist/monologuist are both recognised terms:
http://www.thefreedictionary.com/Monologist
http://www.merriam-webster.com/dictionary/monologist