How Obi-Wan Gained a Seat on the Jedi Council?

During the Attack of the Clones, Obi-Wan Kenobi is just a Jedi Knight with his Padawan apprentice Anakin Skywalker. However, when Revenge of the Sith begins, we see that Obi-Wan is not only a Jedi Master but also has a permanent seat on the Jedi High Council.
How was Obi-Wan promoted?

SOURCE - Brotherhood (Mike Chen)

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