In the original Beauty and the Beast, the reason everyone loves Gaston is basically because he's "hot". (I put that in quotes because a real-life person with those proportions would be TERRIFYING.) But Luke Evans says there's more to the good-looking villain in the new live-action adaptation than what was on screen in 1991.
Evans spoke to EW about his character, and the background that actually justified Gaston's "local hero" status:
The fact of the story is that Gaston is a war hero and an army captain, and the only reason he's got this celebrity status in Villeneuve is because when he was about 16, he protected the town from a pack of Portuguese marauders in 1740.
He's basically been a local legend since he was 16. Yeah, that might explain some stuff.
Evans went on to say that his first interpretation of Gaston was going to be much darker than the version the movie actually ended up using, as the character's PTSD would form the basis of a lot of his actions. After Evans' audition, the director called back and said they were going to try it again, but closer to the original, less dark Gaston. However, the actor believes PTSD still shapes the character a bit:
He probably does suffer from PTSD, which he manages to keep under wraps because he has people like the villagers and LeFou and the girls who puff him up and make him feel sexy and wanted. But below that is a broken human being. He's jaded, and the second he realises that he's not going to get what he wants, this military creature comes out of him.
There's also something that explains LeFou's (Josh Gad) devotion to the character in a way that is so much better than that if he just had a crush. According to Evans, LeFou also went to war with Gaston and was with him for all his heroic moments, so he has a reason to insist on Gaston's perfection.
That's actual depth! Gaston has always felt harder to make interesting than other Disney villains because he was such a buffoon, and it really didn't make sense that everyone in the village just worshipped him when he was transparently a self-absorbed dick all the time. At least now we know why he got away with it and why he swings from a mere jerk to leading a mob so easily.