One Pieceβs Wano arc has been very important to the story at large. From Kozuki Odenβs flashback to reveals only present in the manga as of this writing, many important One Piece lore concepts have been introduced or expanded upon in the current arc.
Of particular note are the various characters introduced throughout the arc, who have each played an important role in its progression thus far. While their importance to One Piece as a whole can be debated, there's no arguing the significance of their presence and actions within the Wano arc.
Here are the ten most important characters introduced in the Wano arc so far, in no particular order.
Kozuki clan dominates most important characters in One Pieceβs Wano arc
1) Yamato

As a former friend of Ace and someone striving to become the next Oden, Yamato is undoubtedly one of the most important characters introduced in One Pieceβs Wano arc. Her role going forward in the story will either be to join the Straw Hats or to protect Wano as its new guardian deity, and both roles are incredibly important.
Her knowledge of Odenβs travels and being in possession of his logbook further increase her importance within the Wano arc.
2) Kozuki Oden

Kozuki Oden is arguably the single most important character introduced in One Pieceβs Wano arc. His death at Kaidoβs hands set the stage for the arc's progression and goals, as well as gave reason for the Straw Hatsβ presence in the country.
His flashback was also incredibly important, giving fans a glimpse into Rogerβs era, as well as teasing whatβs on the last island of Raftel. Thereβs little argument against him being one of the most important characters introduced in the arc, and possibly even the single most important.
3) Otama

The main factor of Otamaβs importance throughout the Wano arc is her serving as further inspiration to Luffy to liberate Wano. Her having known Ace is also somewhat significant, but the main importance she holds is serving as inspiration for One Pieceβs protagonist.
She also plays a somewhat significant role in the Onigashima Raid, which has yet to be revealed in the seriesβ anime.
4) Kurozumi Orochi

Kurozumi Orochiβs betrayal of Kozuki Oden and desire of vengeance for the Kurozumi clan against the Kozukis is one of the most important factors of One Pieceβs Wano arc. It sets the stage for the death of Oden 20 years prior, as well as establishes him as one of the arcβs main antagonists.
While he doesnβt serve much of a role outside of these two factors, theyβre still significant enough to count him as one of the most important debuting characters of the Wano arc.
5) Hyogoro

Hyogoro is responsible for teaching Luffy how to utilize Ryou, which is a form of Advanced Conquerorβs Haki. As seen in the most recent One Piece anime episode, this is incredibly important as it gives Luffy a means of damaging Kaido during their fight.
Beyond this, heβs also an integral figure in the Onigashima Raid for the general forces, serving as both leader and inspiration for them during the battle.
WARNING: ONE PIECE MANGA SPOILERS IN FOLLOWING SECTION
6) King

Kingβs introduction in One Pieceβs Wano arc serves two main functions. First, he serves as a means of introducing the Lunarian race into the series lore, which will likely be expanded upon in future arcs.
The second significant function he serves is as a means of Zoro activating his Advanced Conquerorβs Haki to beat him. This allows the Straw Hat swordsman to fully come into his own as both a character and a fighter, which will no doubt be significant in the storyβs final stages.
7) Queen

Queenβs introduction during the Onigashima Raid as a former member of the SADS research group helps to paint a picture of how the Beast Pirates came together. Kingβs flashback to meeting Kaido shows that the two met in a government research facility, which is also likely where they met the third Calamity.
Like King does with Zoro, he also serves the purpose of elevating Sanjiβs power to a new level which is necessary for the storyβs final stages. These two roles solidify him as one of the most important characters introduced during One Pieceβs Wano arc.
8) Shimotsuki Yasuie

Shimotsuki Yasuieβs tragic death and last words are the main factor of his importance in the arc. With his final words, he keeps the hopes of the Onigashima Raid alive, despite not being given the opportunity to live and see its success.
Beyond this, he and the other residents of Ebisu Town serve as further inspiration for Zoro in the upcoming raid. Their being forced to eat defective SMILE fruits and lose the ability to show emotions as a result clearly and deeply affects the Straw Hat Swordsman.
9) Komurasaki/Hiyori Kozuki

Komurasaki, later revealed to be Hiyori Kozuki, is undoubtedly one of the most important characters introduced in Wano. While her full role has likely yet to come to fruition, itβs incredibly likely sheβll end up as the next shogun of Wano, reclaiming the throne for the Kozuki family.
While Momonosuke is also an option, heβs still incredibly mentally young, even if Shinobu was able to age him physically. As a result, Hiyoriβs full and most important role will likely be as the next leader of Wano.
10) Whoβs Who

Finally, Whoβs Who plays a massively important role in the wake of Luffyβs true Devil Fruit being revealed. He gives readers their first hints that the Gum-Gum Fruit is special, while also introducing Nika the Sun God and setting the community ablaze.
While this is likely his only role of importance in the arc, the importance of these actions cannot be understated. They set the stage for the biggest reveal in One Piece yet, and arguably one of the biggest in animanga at large.