Roronoa Zoro is the swordsman of the Straw Hat Pirates and also the second in command of the crew in One Piece. Being the first person to join Luffy's crew, Zoro holds tremendous importance in the series.
As with each character in the crew, Zoro's character designs and outfits often compliment his personality and hint at both his character and his way of looking at life. While Zoro certainly doesn't go through as many outfit changes in One Piece, there are quite a bunch of interesting details about him that only a few fans have noticed.
7 Haramaki
One of the very few constants about Zoro's clothes is the Haramaki that he always wears on his belly. This was first seen during his introduction in Shell's Town and it has remained a part of his character design ever since.
Zoro's green Haramaki is one of the things that stand out the most about him, as evident from the fact that Koby recognized him from looking at it when he was tied in a Marine base on the island. Even after the two-year timeskip, Zoro's Haramaki hasn't changed, meaning it holds great importance to his character and will likely remain a part of him forever.
6 Pre-timeskip Outfit
Before the two-year timeskip, Zoro's outfit changed quite often. While his Haramaki always remained a part of him, along with his trousers and boots, he often changed his shirts. His original character design saw him wear a white t-shirt with three buttons, which could be a nod towards him being a user of the Three Sword Style.
With every island, Zoro often changed to different shirts before eventually switching to a different outfit after the two-year timeskip entirely.
5 Post Timeskip Outfit
Zoro went through quite a lot of change after the two-year timeskip. Not only did he grow bigger and more muscular, but he also lost one of his eyes and, interestingly, changed his attire quite a bit. While Zoro did keep his Haramaki, trousers and boots, he started donning a dark green coat that is tied by a red sash over his waist.
He also tucks his three swords into the sash while the bandana that he often wears is tied on his left arm. Zoro's new outfit makes him seem much more mature and indicates how he is more than ready for the perils of the New World and, most importantly, to surpass the World's Strongest Swordsman, Dracule Mihawk.
4 The Bandana
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Roronoa Zoro takes battle quite seriously and growing stronger is one of his biggest motivations in the story. When he engages someone in combat, Zoro often tests their skill first and, upon getting serious, he then dons the black bandana on his head, which is often an indication of him acknowledging the strength of his enemy.
It has also been hinted that he grows stronger upon putting the bandana on and while this has never been explicitly proven, it certainly does improve his focus and determination in battle, making him a force to be reckoned with.
3 Wano Country Ronin
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In the Wano Country arc, Zoro went through a few outfit changes, just like the majority of the crew. He was assigned the role of a Ronin by Kin'emon upon stepping foot in the country and this required him to change from his traditional outfit into one worn by Samurai.
Zoro wore a white yutaka with wavy patterns on the bottom which was held by a blue sash on his waist. Furthermore, on his shoulders, he donned a jittoku haori with the patterns of a dark sun all over it. His Haramaki was the only thing about him that remained unchanged from his previous outfits.
2 The Onigashima Outfit
On Onigashima, Zoro wore a new yet familiar outfit. Just like his post-timeskip outfit, he decided to keep his Haramaki, his bandana, along with his black trousers and boots. The only thing different about his outfit was that instead of a dark green coat, he decided to wear a black one.
The coat was held by a red sash on his waist which carried his swords as well, including the new beloved sword of Oden that he received from Hiyori, Enma. For a short while, Zoro also wore a Beasts Pirates outfit, thanks to Kin'emon Fuku Fuku no Mi powers, however, this attire didn't last long at all.
1 The Earrings
One of the very few things that have never changed about Zoro's character design is his earrings. On his left ear, he wears three identical gold earrings. While on the surface they look like just another accessory that one would wear, however, they certainly do carry some significance.
The three earrings are an indication of the Three Sword Style that he has mastered over the years. It is highly likely that Zoro will always wear these earrings even when he is much older, as implied by Eiichiro Oda's character designs of him at the age of 40 and 60.