At the core of Attack on Titan are the Titans themselves. These massive monstrosities continually try to rip their way through every city built by humans, eating them like popcorn along the way. It actually gets pretty gruesome at times. That's why the Survey Corps exists along with Eren Yeager who can change form into the Attack Titan and help in their defense of humanity.
The worst Titan of them all was Bertholdt Hoover, aka the Colossal Titan. While others have been able to make the transformation, Bertholdt blew viewers' minds when they found out it was really him. That being said, there were signs along the way of Bertholdt's true identity.
10 He Stayed In The Background
Like most antagonists with a lot of power, Bertholdt waited in the background of the story. Very few people, if any, were aware that he was the Colossal Titan. That was probably a good call on his part as that's the kind of secret he didn't want getting out until the time was right.
While he gained increasing prominence as the series went on, Bertholdt managed to hide in plain sight for a long time. That alone should have been a tipoff that something was up with him.
9 He Was Quiet & Kept To Himself
Whenever witnesses or neighbors in movies or TV series talk about someone surprising doing something strange, they always seem to mention that that person had always been quiet and kept to themselves. It's a straight-up cliché at this point, but it's also one that works.
A phrase like "quiet and kept to himself" certainly applies to Bertholdt. He wasn't the most lively guy a lot of the time, which was because he was trying to hide a massive secret. In fact, it wouldn't be out of line to suggest that his secret was colossal.
8 He Was Prone To Fits Of Rage
The second part of the "quiet and kept to himself" trope is usually the extreme levels of anger that accompany it. Any character who has those traits also seems to have a nasty side, one that pops up at what can appear to be surprising times.
That was certainly true of Bertholdt, who would fly off the handle in some pretty rough situations. Often, he was set off by someone threatening the few friends he had. Other times, the reason seemed more arbitrary. And this was without the Colossal Titan cutting loose.
7 He Was Detached & Indifferent To Humanity
There was another subtle clue to the type of person Bertholdt truly was right in front of everyone's eyes. He might have had a few people he seemed to genuinely care about, but he generally didn't appear to care that much about most other people.
That seems counter-intuitive given his chosen profession, but Bertholdt had his own reasons for doing what he did. This didn't change that he continually displayed a cold demeanor when it came to the plight of humans in this world.
6 He Stopped Caring About His Friends
While Bertholdt started off as quiet, indifferent, and detached, that didn't mean that he didn't have connections to some people. He cared deeply for anyone who had a genuine connection with him, and this was especially true in regards to his friends.
Over the course of the series, Bertholdt's coldness began to apply to even his closest friends. He built more and more distance into these relationships, eventually treating them the same way he did everyone else.
5 He Had A Weird & Awkward Body At Any Size
There is a surprising amount of variation in the look of each of the Titans. They range greatly in size, body shape, faces, and even hair. What they have in common is that they are massive monstrosities who want to eat people.
In the case of the Colossal Titan, the differences were even larger. Naturally, it was one of the biggest Titans around, but it also had a pretty awkward body. Some of those traits were mimicked in Bertholdt's body, as well, like their oddly long arms.
4 He Acted Like A Villain Regardless Of His Form
It was incredibly easy to treat the Colossal Titan as a villain. This was a gigantic monster who was devoted to knocking down the walls protecting humanity so he could snack on them to his heart's content.
But even in his human form, Bertholdt was a nasty character. There were times where it felt like he was up to something much deeper, like he was a wolf in sheep's clothing. As it turned out, he was a Titan in people's clothing.
3 He Was Remorseless In His Actions
Bertholdt wasn't someone who walked a true and virtuous path. That being said, doing that honestly would have made him even more suspicious. But even when he did something that was beyond horrific and destructive, it didn't appear to bother him at all.
He rarely, if ever, showed remorse for anything he did, no matter how good or evil that action was. As Bertholdt's cold, detached view of the world increased over time, that only got worse and worse.
2 He Threatened To Kill All Humans
As Attack on Titan progressed, Bertholdt started to change in some not-so-good ways. He became more vocal, uncaring, and distant, causing him to appear to be more villainous. As fans would eventually find out, that was very much true.
But this became much, much more apparent when he started threatening to kill all humans. That's usually a dead giveaway that a character is not only a bad guy, but that he or she might be the big evil of the show. That definitely was the case with Bertholdt.
1 He Was Constantly Sweating
At first glance, someone like Bertholdt sweating a lot might come across as pretty innocuous. It's kind of odd, but still a seemingly minor detail. In truth, it turned out to be a rather major hint as to his true nature.
The Colossal Titan was constantly producing steam in a strangely similar pattern to how Bertholdt would sweat. It might not have been the most obvious clue, but it was one of the few visual cues that led fans to the truth about the character before the reveal.