Greatest failure?

What character would you say has failed the hardest overall?

Maul is the first that comes to mind

Yoda.

Anakin Skywalker.

Palpatine, followed by Anakin. Palpatine literally snatched defeat from the jaws of victory by just not being able to read the room.

Anakin

Anakin. Even more so in canon, where his final redemption and victory over Sid was apparently very short-lived.