Steve "the Hair" Harrington is Hawkins' resident popular boy. In season 1 of Stranger Things, he's friends with all of the other popular or "cool" students at the high school and trying to date Nancy Wheeler, one of the smartest girls in school. They come from pretty much opposite worlds and have very different attitudes to life and different ways of expressing themselves.
With Nancy, Steve shows his best and his worst sides, but the relationship peters out quickly. In season 2, Steve befriends Dustin, which turns out to be the iconic duo nobody realized they needed to see. With Dustin and the other kids, Steve is protective, kind, considerate, and hilarious. Audiences have now seen the best and worst of Steve.
BEST: Courage
Perhaps he's a little full of himself, but it can't be denied that Steve also has a lot of courage. He's not afraid of what others will think of him, even his so-called friends, Tommy and Carol. In season 1, he breaks away from them and tries to support Nancy and Jonathan.
In season 2, his courage becomes apparent in a more physical way. Since he's so bored, he's dying to get in on the action and doesn't hesitate to show off his batting skills against the demodogs. Unfortunately, they don't prove to be all that useful, and he ends up hiding out with the kids on a bus. Still, in season 3, Steve urges Dustin to save himself while he's left to the mercy of the Russians.
WORST: Arrogance
This is something that Steve grows out of - or at least, begins to - by the third season of the show. Everyone calls Steve the king of Hawkins High, and he knows it.
He thinks that he's better than everyone else, especially people like Jonathan who don't really have any friends. He has a hard time accepting that Billy is taking his place as the king of the school.
BEST: Compassion
For all of Steve's attempts to act cool and impersonal, he still manages to show a lot of compassion, too. In the first season, he tries to make Nancy feel as comfortable as she can, always willing to take things slow and help her study if that's what she wants.
He even sticks by her in her search for Barb and accompanies her to visit Barb's parents after she's gone. He shows a lot of sympathy when speaking with Dustin and is his only friend when he first returns to Hawkins after Camp Know Where.
WORST: Judgmental
Steve is quick to make up his mind about things. For example, he assumes that there must be something wrong with Jonathan just because he's an introvert and doesn't like getting involved with the other students.
He also assumes that Jonathan is a pervert and that he and Nancy are getting together. In fact, he has a lot to say about the Byers family that isn't true and isn't kind.
BEST: Protective
Part of the reason Steve became such a fan favorite after season 2 is his new display of protectiveness. Even though he's kind and caring towards Nancy, his older brotherly side doesn't come out until he befriends Dustin.
He tries his best to protect the kids, but there are too many of them and only one of him, so they usually end up overpowering him. Steve even gets into a fight with Billy in an attempt to protect Max and Lucas.
WORST: Self-Conscious
Though he's cocky, Steve also has many insecurities. In fact, his faux self-obsession may be a way for him to conceal his insecurities. For one, he very quickly becomes jealous when he sees Nancy spending time with Jonathan, even as friends.
His insecurities become clear in the third season when he's unsure about pursuing Robin. At first, he makes up the excuse that she's not cool enough for him, which he probably does believe to an extent, but it'd not the real reason for his hesitation. When it comes to forming a real emotional connection, Steve is nervous.
BEST: Responsible
Responsibility is something Steve develops over time. he certainly doesn't start the series as someone who can be described as responsible, but as he grows, he also learns that being mature means holding yourself accountable.
For instance, he actually tries to take good care of the kids. He also holds himself accountable for his prior bad choices. He apologizes to Nancy long after it's necessary, buys Jonathan a new camera, and by season 3, he's practically a dad to most of the kids.
WORST: Jealous
Steve hurts Jonathan because he's already jealous of what he and Nancy have before they even have anything. He sees them sleeping together after they fight the Demogorgon and misunderstands what he's seeing.
The truth is, they're just two scared teenagers who are starting to form a sweet friendship. Meanwhile, his relationship with Nancy isn't based on any real emotional connection. He's jealous again in season 2 and wastes way too much time trying to win Nancy back.
BEST: Accepting
This is another thing that Steve has had to work on over time, but it's clear, especially in season 3, that he is a kinder and more accepting person. However, hints of his kindness can be seen even in the first season.
Firstly, he's quite considerate when it comes to Nancy. There's also his relationship with Dustin, which is full of love and care, even though Dustin is a bit nerdier than Steve's usual crowd. In season 3, he doesn't even question Robin when she comes out to him as gay, showing how much he's grown since season 1.
WORST: Self-Obsessed
No matter how much Steve grows, he just can't seem to get over himself. He may not think that he's the best or coolest person, but he still holds himself up on a pedestal, thinking he's too precious to dirty his reputation.
At the beginning of season 3, his excuse for not wanting to date Robin is that she's in band. Before that, in season 2, he truly believes that he's giving Dustin good advice about relationships and hair, when in fact, Dustin shouldn't have listened to either.