Obi-Wan Kenobi was the apprentice of Jedi Master Qui-Gonn Jon and helped him rescue Queen Amidala from the Trade Federaton blockade of Naboo.
When Qui-Gon was killed by Sith Lord Darth Maul he asked Obi-Wan to train young Anakin Skywalker as a Jedi.
The Jedi council eventually agreed to allow Obi-Wan to begin Anakin's training, although Yoda was not happy about it.
Anakin was a quick learner, although he didn't always do as his teacher Obi-Wan asked him to.
Obi-Wan and Anakin were asked to be bodyguards by Chancellor Palpatine, although Obi-Wan quickly had to leave Anakin with her.
He was investigating an attempt on Padme's life and ended up on Kamino where he learned of a clone army being built, before travelling to Geonosis and being captured.
Obi-Wan Kenobi returned years later
After the clone army and the rest of the Jedi came to the rescue Obi-Wan and Anakin were both defeated in a fight by Count Dooku.
Later Obi-Wan was found on the planet of Tattooine - living as Ben Kenobi - by Luke Skywalker.
He helped Luke link up with the Republic before allowing himself to be killed in a battle with Sith Lord Darth Vader.
Even though he was dead Obi-Wan continued to help Luke from beyond the grave, guiding him to Yoda where he could be trained as a Jedi.