Obi-Wan Kenobi recently expanded the Star Wars prequel lore, by adding more depth to the characters of Kenobi and Darth Vader. However, with newer Star Wars media expanding other interesting characters from that trilogy, it is worth noting how underused they were in the films.
With the likes of Kit Fisto and Plo Koon, who got their due diligence in The Clone Wars, to senators Bail Organa and Padmé Amidala, these characters should have been given more screen time.
1 Ki-Adi Mundi
The Cerean (Silas Carson) was a Jedi Master during the Clone Wars, and a member of the council. Mundi met his end during Order 66 in Revenge of the Sith when he was betrayed by his clone battalion.
Mundi was interesting, as he was a character that completely epitomized what was wrong with the Council. Portraying hubris and arrogance, his characterization was also explored in The Clone Wars television show, as he quickly turned against Ahsoka Tano. But, his screen time in the films was very limited, with his death being the most impactful of the Order 66 sequence.
2 Coleman Trebor
Trebor tried to make a hero of himself during the arena battle in The Attack of The Clones, and attempted to assassinate Count Dooku. But, Jango Fett dispatched him effortlessly.
Admittedly a more light-hearted addition to this list, Trebor's death has taken on new life as a meme in the last few years. His character's pointlessness has been highlighted. It would have been nice for him to have proved himself at least slightly more competent, as he was just a plot device to reiterate Fett's ability.
3 Bail Organa
First appearing in Revenge of The Sith, senator Bail (Jimmy Smits) managed to outlive the turmoil of Order 66. After conspiring with Obi-Wan Kenobi (Ewan McGregor) and Yoda about the upbringing of Anakin and Padme's twins, Bail adopted the girl, Leia, to live on Alderaan.
Bail was fantastic, and underused solely because he wasn't introduced until the final movie of the trilogy. It has been great to see Smits reprise his role in recent years, most notably in Obi-Wan Kenobi.
4 Aurra Sing
Sing was a force-sensitive Palliduvan turned bounty hunter. She only made a cameo in The Phantom Menace, during the pod-racing sequence.
Hindsight is a massive factor. Sing's characterization was expanded more thoroughly in The Clone Wars, where she was involved in the storylines of Cad Bane and most notably Boba Fett, who was grieving the loss of his father. She should have been utilized more.
5 Kit Fisto
Fisto was a Jedi Master that almost outlived the prequel trilogy. However, as one of those that looked to arrest Chancellor Palpatine (Ian McDiarmid) on Coruscant, he was killed.
Fisto was offered minimal screen time across the films, with his smiling meme during the arena battle being an obvious highlight. His death was also quite laughable; despite lasting against Palpatine for longer than the other two Jedi Masters, he wasn't able to present much of a challenge. This one is more frustrating, as Fisto was an incredible character in The Clone Wars.
6 Plo Koon
The telekinetic Jedi Master was also a victim of Order 66. His starfighter was shot down by his clones and exploded, on the planet Cato Neimoidia.
This one had very similar reasons to Fisto's placing on this list. Koon was perceived as one of the Masters that didn't let the power get to his head, as his characterization was fleshed out during The Clone Wars. His relationship with Ahsoka was lovely to watch. His death scene was only reduced to mere seconds.
7 Count Dooku
At the end of The Attack of The Clones, Dooku (Christopher Lee) bested Anakin by chopping off his arm. In Episode 3's rematch, Dooku was beheaded by an increasingly more powerful Skywalker.
Whilst Dooku earned a considerable amount of screen time as the main antagonist of the second movie, it is still Christopher Lee, so there's never enough of him. He was fascinating; not agreeing with the Jedi ideals, his turn to the dark side turned heartbreaking as he realized he was merely a pawn in Palpatine's plan. He was fleshed out even more in animated form. Tales of the Jedi epitomized how underutilized Dooku was.
8 Padmé Amidala
After secretly marrying Anakin, Padmé (Natalie Portman) was pregnant with twins during The Revenge of the Sith. After giving birth, she died of a broken heart, following the discovery of Anakin's devasting turn.
Padmé's death has never felt satisfying. The feisty senator was in the thick of the action during the first two prequel films, but was certainly less involved in the third. To die of a broken heart, she was arguably a victim of not knowing how to dispatch a character that was not in the original trilogy.
9 Darth Maul
Maul, a Dathormian Sith Lord, faced Obi Wan and Qui-Gon Jinn (Liam Neeson) in The Phantom Menace. After murdering Qui-Gon, Kenobi supposedly killed Maul on Naboo, before he was revealed as alive during The Clone Wars.
With The Phantom Menace controversially received back in 1999, it was always universally agreed that Maul was a fantastic villain. His popularity led to his return in animated form, and eventually a cameo in Solo: A Star Wars Story. They prove that Maul's 'demise' was completely premature, with his feud with Kenobi being explored away from the films.
10 Mace Windu
Windu (Samuel L. Jackson) learned of Palpatine's deception from Anakin in Episode 3. After confronting Palpatine, Anakin defended the Sith Lord by severing Windu's arm. Palpatine responded by using Sith electrocution to dispose him.
Whilst Windu was certainly an important character, the fact that he was never in an individual film for longer than Jar Jar Binks was, can justify his place. Windu was interesting as he also epitomized the hubris of the Jedi, and contributed to Anakin's turn. Furthermore, it was sad how underused an actor of Samuel L. Jackson's pedigree was.