4. Plo Koon
Jedi Master Plo Koon appeared in all the prequel trilogy films, but audiences learned very little about him. The Clone Wars television show made up for this by prominently featuring his character in a number of episodes and exploring his relationship with Ahsoka Tano. Plo Koon is actually the one who saved Ahsoka from enslavement and brought her to the Jedi Temple. They maintained a special bond over the years and he continued to be a supportive, wise mentor figure for her.
His leadership with the clone troops under his command also conveyed a great deal about his character. Plo Koon treated the clones with respect and as equals, all of which forged a trusting and communicating team. Both with and without his troops, he showed admirable bravery and wisdom in countless moments during the Clone Wars.
His death during Order 66 in Revenge of the Sith carries far more emotional weight given how audiences truly got to know him during The Clone Wars.