Humid, swampy, and inhospitable, the bog world of Dagobah was the home of the last of the great Jedi Masters. After a fevered vision of Obi-Wan Kenobi on the planet Hoth, Luke Skywalker used the Force to puzzle out the proper hyperspace coordinates to the lost world, hoping to complete his Jedi training at Yoda's hands. There, in the oppressive heat of the swamp, young Luke underwent the first of many grueling tests that would mold him into a Jedi Knight.
Greatest of the Jedi Masters, Yoda was one among the very few to survive the coming of the dark time to the galaxy. Isolation and long contemplation on Dagobah led him to new heights in his understanding of the Force.
R2-D2 (with ratcheting head)
Cheerfully trundling into even the most dangerous situations, Artoo often found himself in deeper than he'd intended. Such was the case when he toppled off Luke's mired X-wing and into Dagobah's sludgy water. Thankfully, he proved to be less delicious than he looked to the local dragonsnake that called the swamp home.
Spirit of Obi-Wan Kenobi
Wise, old hermit and secret guardian of Luke as a child, Obi-Wan Kenobi was struck down by Darth Vader only to become more powerful in the Force than ever before. It was he who directed Luke to Dagobah, and his patience that convinced Yoda to take Luke on as a student.
Luke Skywalker (with detachable magnet hand and swinging battle action)
Young and brave, Skywalker was a fast and eager learner, but his own impatience and latent anger proved to be his greatest enemies. Despite the guidance of both Yoda and Obi-Wan Kenobi, he was on his own for much of his Jedi training. It was his deep native connection to the Force that allowed him to eventually control his own emotions.
Spirit of Darth Vader
The dark side of the living Force fed on Luke's insecurities to produce this hideous manifestation. It was a mental and physical attack that tested his skills as a warrior and his dedication to the light side of the Force; one that seared itself on his psyche for his entire life.