Obi-wan Kenobi was possibly born on the planet Alderaan. He was discovered at a young age by Jedi Master Mace Windu, and was brought to the Jedi Temple. At the age of eleven, he became an apprentice under Qui-Gon Jinn.
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 making their ill-fated attempt to bring the Neimoidians to the negotiating table.
Obi-Wan assumes the responsibility for training young 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 gene donor for the clones, leads him to Geonosis, where the leaders of several large corporations are meeting to discuss seceding from the Republic. There he learns 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 Grand Army of the Republic. He helps lead the rescue of Chancellor Palpatine, who had been captured and is being held aboard the Invisible Hand, the flag ship of the CIS mastermind, General Grievous.
He subsequently leads the Republic forces at the planet Utapau, where the CIS has established a base. During the battle, he kills General Grievous, and the remainder of the CIS leaders flee to Mustafar.
Learning of Anakin's turn to the Dark Side of the Force, he tracks his former pupil to Mustafar. The two engage in a lightsabre duel which ends with Anakin severely wounded. Obi-Wan leaves his former friend for dead and returns to Amidala's ship. He rendezvous with Yoda and the leaders of what will become the Rebellion against the Galactic Empire. There he takes charge of Padmé and Anakin's son, Luke, taking him 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 interrupted when their ship, the Millennium 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 Dagobah. He further tries to persuade Luke not to end his training prematurely and fall into the trap set by Darth Vader on Bespin.
Return of the Jedi
Obi-Wan's ghost appears briefly to comfort Luke after the death of Yoda and confirm that Darth Vader is indeed Luke's father.