By "uses captivating words", what precisely do you mean? Eloquent speech in general, or does he always sound like he's deliberately trying to entice people into doing something?
And what's giving you difficulty? Coming up with his dialogue? Figuring out how he'd react to a certain situation? Both? Something else?
Sorry for all the questions, but I just want to be clear.
Anyway, sometimes when I'm having difficulty figuring a character out, I try taking personality quizzes and the like as though I am that character. (Obviously this doesn't work if you don't know
anything about the character's personality, as you do need at least some sort of baseline, but then you probably couldn't call it a character without knowing something about it anyway.) I don't mean those silly things pasted all over Quizilla or most Pokémon websites; you can try those if you want, but they're generally too shallow and simple to account for a wide variety of characters (my asexual characters mentally rage over all those "omg your crush just asked you out what do you do?!?! :D" questions). Really detailed questionnaires, though, like the personality type quiz on
MyPersonality, give you a lot of different situations to think about. I also found
this one on deviantART, and it's relatively interesting. I even have a book,
What Would Your Character Do, that sets up thirty distinct scenarios and tries to you figure out how your character would react. Search around for things like this and you'll probably find a lot of others that could be even more useful to you.
No one quiz/interview/questionnaire/whatever is ever going to be totally relevant to what you're writing, but as you answer the questions you can it gets you thinking about "yeah, I do think this is what my character would do here" or "...eh, would he really say that?" Even questions or answers that are entirely irrelevant can be helpful (again, for example, how would an asexual character react to being asked "do you have fun with your significant other?" and seeing that the only options are "I luff them!", "All we do is screw around", and "I'm totally cheating on them with someone else"?). That, in turn, can be helpful when trying to fill in any blanks in your character's personality.
Characters tend to develop their own personalities the more time you spend with them, so spending that time getting to know them is usually a good course of action. Ask them questions, put them in exciting or uncomfortable situations, maybe even try some stream-of-consciousness writing as the character, and see how your mind has them respond.