I'm not using Obi-wan in my version, but I'd expect from the OT that he fought in the clone wars because he was an idealist who genuinely believed that he was making a difference, which is why he became a Jedi, and also a general. He became a highly decorated war veteran, but was reckless in his "crusade" for justice. He discovered Anakin Skywalker, and realized that here was a chance to convert a truly powerful individual to his cause, and so he rushed Anakin's training in an attempt to bring him quickly to his full power. This fails, and when Anakin turns to the Dark Side, Obi-wan learns to take things slower, and gains patience. He goes to Tatooine to watch over Luke, and decides not to interfere in his life the way he did with Anakin. However, events force him to go back to his old methods of teaching, where he gets results at the expense of the student's understanding. He teaches Luke a great deal in the short time available, but realizes that he isn't the best teacher for him, and sacrifices himself to give Luke time to escape the Death Star. That's his story in a nutshell, at least from my point of view!