The Rebel

Both series (The Rebel and Taxi Driver and sequels) feature vigilantes operating outside the law. The ML in both series is part of an organization or gang that carries out acts of justice on behalf of others. Both Hong Gildong and Kim Do Gi employ similar techniques to deceive villains (disguises, posing as their employee/servant to gain their trust, etc.). Both series feature plenty of action, and The Rebel also includes a small fantasy element.

Rebel: Thief who stole the people is another historical drama made by the same director of missing crown prince (Kim Jin Man)

Both dramas are about unconventional heroes trying to save the people from a corrupted king, so many twists and turns, keep you guessing what will happen next.

Similar tone, historical setting, slow pace, and interesting characters. The ML's personality also seemed similar to me.

Both dramas have and interesting and intriguing story, magnificent acting, as well as deep and growing characters, well-fitting music and beautiful cinematography.