Obi-Wan Kenobi
Obi-Wan Kenobi is a Jedi Knight of the Galactic Republic. He taught both Anakin and Luke Skywalker about the Force.
The Phantom Menace
Chronologically in Star Wars Obi-Wan first appears as Qui-Gon Jinn's apprentice as the two of them are investigating the Trade Federation's blockade of Naboo and failed attempt to bring the Neimoidians to the negotiating table.
Obi-Wan assumes the responsibility for training yound Anakin Skywalker upon the death of his master, Qui-Gon.
Attack of the Clones
Obi-Wan is responsible for investigating the attempted assassination of senator Padmé Amidala. The investigation leads to the discovery of the clone army, commissioned shortly after the events of TPM. Tracking Jango Fett, the donor for the clones leads him to Geonosis where the leaders of several large corporations are meeting to discuss seceeding from the Republic, and that Count Dooku is apparently orchestrating the movement. These discoveries lead to the Clone Wars, with Dooku leading the disaffected corporations in the creation of the Confederacy of Independent Systems
Revenge of the Sith
Obi-Wan, along with several other Jedi, has become a general in the forces of the Grand Army of the Republic. He helped lead the rescue of Chancellor Palpatine who had been captured and was being held abord the Invisible Hand, the flag ship of the CIS mastermind General Grevious.
He also led the attack on the planet of Utapau. During the battle, General Grevious is killed by Obi-Wan and the remainder of the CIS leaders flee to Mustafar.
He learns of Anakin's turn to the darkside of the Force and tracks his former pupil to Mustafar. The two engage in a lightsaber duel which results in Anakin being severly wounded. Obi-Wan leaves his former friend for dead and returns to Amadila's ship. He rendezvous with Yoda and the leaders of what will become the Rebellion against the Galactic Empire. Here, Padme gives birth to Luke and Leia who are split up, Obi-Wan taking the infant Luke to Tatooine to be raised by the Lars.
A New Hope
Obi-Wan rescues Luke Skywalker from an attack by Sand People and learns of the desperate situation the rebellion is in with the completion of the Empire's new terror weapon, the Death Star. Obi-Wan invites Luke to accompany him but Luke is reluctant until he learns that Imperial Stormtroopers have killed his aunt and uncle and destroyed his home. Obi-Wan begins teaching Luke about the Force but the training is interupted when their ship, the Millenium Falcon is captured by the Death Star and Obi-Wan is killed by Darth Vader. However, his "ghost" continues to give Luke guidance from beyond, helping the young Skywalker use the Force to destroy the Death Star.
The Empire Strikes Back
The Ghost of Obi-Wan appears to Luke Skywalker on the planet Hoth instructing Luke to seek out Yoda on Degobah. He further tries to disuade Luke from ending his training prematurely and not fall into the trap set by Darth Vader on Bespin.
Return of the Jedi
Obi-Wan appears breifly to comfort Luke after the death of Yoda and confirm that Darth Vader is indeed Luke's father.