Almost every character gets a chance to showcase their level of intelligence at one point or another on The 100. The show is all about war, strategy, and survival, so intelligence is key. Not every character is born to be a leader, but it's often the underdogs who end up shining the most.
Some characters may have more knowledge, simply because of their age or education, but that doesn't mean they have the same level of emotional intelligence as others, which is also important. Relative to their age and circumstances, some characters' level of intelligence may come as a surprise.
John Murphy
Murphy may be evil for much of the series, but he has a clear agenda. He knows exactly who he is and what he's willing to do to get what he wants, even if it means sacrificing his soul.
However, he's too reckless to really be considered intelligent. He does things without thinking, which often gets him caught, or hurt, or hurts other people. Most often, it's actually the latter.
Bellamy Blake
Bellamy often seems like Clarke's second-in-command; he knows almost as much as she does of war, conflict, strategy, and peacekeeping. In fact, in some ways, he knows more.
He evolves a lot over the seven seasons, sometimes standing firmly by Clarke, at other times radically opposing her, or choosing his own path and pushing for peace. He wants humanity to do better, but he always falls back into his old ways and turns to violence. All in all, Bellamy proves himself to be narrowminded in his thinking and doesn't always have the temerity to carry out tough measures.
Echo
For all of her toughness, Echo often thinks with her heart rather than with her head. She's not willing to let go of past experiences, including her relationship with Bellamy - even when it's long over.
She grows a lot from the violent Grounder she appears to be when viewers first meet her. By season 7, she's more mature and emotionally stable, but when it comes to battle, she acts on spur-of-the-moment feelings before thinking things through logically.
Octavia Blake
Octavia is hard to gauge, simply because she seems to be a different person every season. Her evolution is complex, and the way she thinks and processes things changes all the time.
At times, she does what she wants, when she wants. At other times, she takes on the role of leader, making sure her people survive. Even if she makes mistakes, she somehow succeeds in getting people to follow her and, for the most part, to survive. By the last season, she seems to have learned from her past experiences and becomes a selfless, caring young woman, demonstrating a high level of emotional intelligence, as well.
Indra
Indra displays a level of intelligence far above most of the people around her, first when she's a Grounder, and later when she joins forces with Wonkru. She's a master strategist but tries to encourage her people to withdraw from violence when possible. As she mentors Octavia, she sees that she may have gone too far in her training (though it's not entirely her fault).
Nevertheless, Indra understands that Octavia is no longer the same person she was and that something needs to be done about it. Indra also attempts to make things right with her daughter in the final seasons. In general, she has a more open mind about the way Wonkru should live. That doesn't mean that she never makes mistakes, and it certainly doesn't mean she always learns from them.
Marcus Kane
Though Kane's methods are often questionable, viewers can't deny that he keeps things in order on the Ark. During his time on The 100, he grows a lot and eventually reevaluates his previous choices.
When he's on the ground, he comes to understand that survival isn't the be-all-end-all. He also sees that survival can take on many forms. In the end, Kane becomes something of a peacekeeper and the moral compass for many other characters. When everyone else is focused on war and bloodshed, he seems to be one of the few characters still connected to his humanity.
Clarke Griffin
Like any leader, Clarke has a lot of decisions to make. Sometimes, though, she makes the wrong choices, and sometimes she makes choices for other people. Of course, these moments take a big toll on Clarke and everyone at her mercy, like those locked inside Mount Weather.
Outside of her role as Wanheda, before she becomes any kind of leader, she already proves herself to be highly intelligent. She's a logical thinker with a surprising breadth of knowledge on everything about survival on Earth. It's clear that she paid attention in Earth Skills back on the Ark, and she continues to learn on the ground.
Abby Griffin
Abby is very successful as a medic, and her high level of intellect is probably why she and Raven form such a strong bond. She clearly knows a lot about the medical field and has strong morals.
However, she loses herself when she develops a drug addiction. Even before this, though, she fails to be a good mother to Clarke on several occasions. She sends children to Earth to fend for themselves, and even when the adults join them, Abby keeps allowing Clarke and the others to take on adult responsibilities. Still, she displays strong logical intelligence in other areas of her life.
Raven Reyes
Raven is obviously one of the smartest thinkers in the show - she gets the group out of trouble on many occasions, from the first episode to the last. But Raven's intelligence is more than book smarts and logic.
As she evolves and faces heartbreaks and other life-changing events, Raven's morals become more and more entrenched. She stands up to Clarke on several occasions, choosing her own path that she believes will serve the greater good and keep her loved ones safe.
Monty Green
Though the show is about conflict, it's intelligence that often saves the day. Monty is always thinking up clever ways to get himself and his friends out of danger. Especially when he works with Raven, these plans are usually a success.
Also like Raven, Monty's intelligence extends to morals and identity, as well. Though it takes him a while to get there, Monty knows exactly who he is and what he stands for. He chooses his life with Harper, knowing what it means, and knowing that his "sacrifice" will save all of his friends.