One Piece has an extraordinarily large cast of characters. Despite having over a thousand chapters, Oda humanely cannot give every character the same amount of screen time. The emphasis is mainly on the Straw Hats and their adventures, so the other characters have to settle for a limited role.
There is no shortage of characters in One Piece, who could easily have been used more before they were killed or written off. Of course, the series has not finished yet, but there is no guarantee that these characters will be utilized in the future.
9 Dracule Mihawk
Dracule Mihawk is known as the "Strongest Swordsman in the World," which makes him one of the strongest characters in the series. He was the first Shichibukai to be introduced and he made his debut in the Baratie arc.
Mihawk's strength is unquestionable as he displayed his skills during the Summit War and he was among the few characters who managed to remain unscratched throughout the war. It remains Mihawk's biggest involvement so far in the series, which is clearly not enough for someone as strong as him.
8 Boa Hancock
Boa Hancock is the captain of the Kuja Pirates and the current empress of Amazon Lily. She rose to fame just after her first voyage and the World Government recognized her as a threat, so they offered her the position of a Shichibukai.
Boa possesses all three types of Haki, and she has an overpowered devil fruit. She hasn't had the opportunity to display her full strength, and it might make the fans worry as One Piece is nearing its conclusion. The next few arcs should have Boa Hancock in them so that she can show the community what she is truly capable of.
7 Ryokugyu
Along with Fujitora, Ryokugyu is the latest addition to the Marines. He joined the Navy as an Admiral and his first appearance did not come until the Levely arc. It was not even a full appearance, Oda only revealed Ryokugyu's silhouette.
It was later revealed that Ryokugyu and Fujitora had clashed against Sabo and three commanders of the Revolutionary Army. The outcome of their fight is unknown, but that will undoubtedly be revealed in the next arc. Meanwhile, Ryokugyu remains powers remain a total mystery, and he has not been too involved in the story.
6 Chopper
Often overlooked as just the harmless pet of the Straw Hat Pirates, Chopper is easily one of the most underappreciated and underused characters in the series. Chopper is the doctor of the crew, and he is seriously talented.
With his knowledge of medicine, Chopper was able to create the "Rumble Ball," which bolstered his physical attributes. In comparison with the rest of the crew, Chopper could be utilized more. He is usually limited as backup, but he definitely deserves more involvement in fights.
5 Monkey D. Dragon
As the founder of the Revolutionary Army, Dragon is considered the "Worst Criminal in the World." He aims to free the world from the clutches of the evil World Government and so far he has managed to free a few kingdoms.
The fans know almost nothing about Monkey D. Dragon— his past, powers, etc. all remain a mystery. Also, considering that he is the head of the Revolutionaries, he deserves to be more involved, however, the fans have only seen Dragon on a handful of occasions so far.
4 Urouge
Urouge is undoubtedly the least appreciated member of the Worst Generation. He possesses a strong paramecia type devil fruit that allows him to convert physical damage into strength.
With his devil fruit power, Urouge was able to beat Charlotte Snack, who was a Sweet Commander at the time. Apart from a few appearances, Urouge has rarely been included in the story.
3 Smoker
Smoker is a Navy vice-admiral and a close friend of former Navy Admiral Aokiji. Ever since his introduction in the series, Smoker has constantly been chasing Luffy. Unlike most Marines, Smoker has a sense of honor, and he does not believe in "Absolute Justice."
Smoker does not like to follow the dubious orders that he often receives from his superiors, and this makes Smoker an interesting character. His last relevant appearance in the story came during the Punk Hazard arc.
2 Koby
Many fans considered Koby to Luffy's equivalent, but so far they have been proven wrong. Koby was rescued by Luffy after which he joined the Marines and trained under Garp. The training led to Koby becoming stronger and thus, earning promotions in the process.
Currently, Koby is a Marine captain and a member of Team SWORD. It is unknown whether Koby will be utilized in the Wano Country arc or will he be a part of future arcs.
1 Kizaru
Kizaru is the oldest Marine Admiral. He made his first appearance during the Sabaody Archipelago arc, where he almost defeated all the members of the Worst Generation on his own. Kizaru has the power of the Pika Pika no Mi, which allows him to create and control light.
Since the Summit War, Kizaru has not been involved in any other fight. He tried to make a move and get involved in the fight in Wano, but he was stopped by Akainu.