@Joshua  
Dunno about drunkard, but he was definitively of questionable morals.  
In particular, he’s frequently an openly Pagan advisor/whatever to a strictly Christian king (and kingdom)  
Imagine if Bush had an openly Muslim guy as one of his top assistants, it’d rub quite a few of his Christian supporters the wrong way (Bush being the latest President that seemed to be elected at least partly because of how Christian he was. Trump may or may not have had some Christian support, while Obama was probably opposed by the more fanatical Christians, but Bush was definitively strongly supported by bible-thumpers)  
From what little I remember of what little I’ve read about him, usually in work that’s a derivative of a derivative (as in, someone did their own spin on a story that’s already someone else’s spin on a yet earlier version, adding on more changes), Merlin also tends to have a theme of struggling to act in the best interests of the kingdom - he almost always succeeds, but with far more effort than Arthur seems to need (Arthur still works hard, but he works hard while accomplishing his tasks. Merlin works hard just to set the goals at all, rather than giving in to the temptation of ‘screw England, I am the Great Merlin and have more important matters and/or deserve more reward’)  
I think he’s literally half evil, in terms of heritage - half demon, sometimes, and just half ‘magical Pagan’ other times, but either way he usually doesn’t agree entirely with the morals every other mayor character on the Kingdom’s side have (and it’s usually mutual - Merlin’s an immoral part-Pagan who doesn’t follow good Christian behavior, but everyone else’s an immoral Christian who doesn’t respect the land, magic, and a bunch of other stuff)
 
Trying to use Google to fill in the gaps in my memory wasn’t very successful - turns out, he’s far more vague and has far more interpretations than Loki, who I got pretty decent info on when I tried to double-check my info on him a few months back (in the context of making sure ‘Loki Wildfire’ was not a nickname that was already given, yet one that makes sense)

I loved that scene.

@Joshua  
He’s been a wacky weirdo in Disney’s animated movie on the lore, some immortal black guy in Once Upon a Time, and a super serious child born of a demon and human in some movie I watched once in high school.  
I don’t think there is any real solid characterization for him now, like Santa Claus. Just whatever the writer wants him to be with a few recognizable traits shared between them.

Was Merlin REALLY a drunkard in Arthurian lore? I’m only asking in case Transformers 5 screwed up his character.