Umbara, known as the "Shadow World" due to the rays of its sun never completely reaching its surface, is perpetually dark. The native wildlife have adapted to survive in such gloom, making the planet perpetually dangerous. Umbara was once part of the Galactic Republic, represented in the Senate by Senator Mee Deechi. Later in the Clone Wars, the planet's loyalty wavered and the natives of Umbara allied themselves with the Separatists, bringing their extremely advanced technology to the Separatist Alliance.
During the prolonged campaign to retake Umbara, General Pong Krell was given temporary command of the 501st Legion of clone troopers. The gruff, fiercely focused Jedi ordered the clones to conquer the Umbaran capital, no matter what the odds.
The Umbara campaign of the Clone Wars was a trying time for Clone Captain Rex, who had to carefully balance the strict orders of his commanding officers with the well-being of his troops.
Umbara saw the deployment of many clone forces, under the command of Generals Kenobi, Krell and Tiin. On the darkened surface of the planet, these clones charged directly into the advanced technology of the Umbarans.