Guinness agreed at once to meet the director, George Lucas, with a view to playing the master warrior Obi-Ben Kenobi. He thought the part difficult because Kenobi was good. There was a danger of becoming "a bit smug, a bit know-all". Kenobi had to have an "extra sense of what's going on". A short man, as short as Guinness, Lucas was very vulnerable, very nervous of people, and shy. Anthony Daniels, who was to play the robotic character C3PO, said Lucas carried a little black book in which he wrote everything down. His own part of C3PO was full of "terribly corny lines", such as "Curse my metal body, I wasn't fast enough," which were, in an odd way, reminiscent of Victorian children's fiction.

After discussion with Lucas, Guinness agreed to play the role. But they at once had a crisis because, a week or so before shooting, Lucas changed the script which in its previous version had Kenobi appear on page twenty, when he became leader and tutor of a small band of rebels. He then led these on their series of adventures that "culminated in a giant space battle that destroyed the evil empire's principal weapon, the 'Death Star', and ended with Ben Kenobi giving everyone medals".

Lucas had to inform Guinness of the important plot change, and as he did, grew nervous. "Although Ben is the leader," he explained, "I think it might be better if he ... Oh, like kinda died halfway through the picture." Guinness was upset. Understandably so. Actors do not want to play a character that dies halfway through the film; nor did they want to be informed of their premature demise over lunch.

Although he remained extremely civil Guinness later told Lucas he no longer wanted to do the picture. Lucas had a major anxiety attack, which led to another long meeting with Guinness. "I went on and on," Lucas said, "about how important the change was in order to make the story work. And how important it was to have a powerful actor play Ben, especially now that he had so much less screen time. As a writer, he was easily convinced."

As an actor, too, Guinness eventually came around. But he became more than an actor in the film: "an incredible blessing", Lucas was to call it later. The preperation for the filming was on a Herculean scale; what especially endeared Lucas to Guinness was that he himself brought the costumes to London to see if Guinness liked them, while he came to all the fittings.

Daniels spent six very undignified months preparing for C3PO, which sometimes entailed "standing naked in a cold room at Elstree" while they "faxed" his body for its robotic role. When Guinness and his wife Merula arrived at Heathrow in 1976 for the flight out to Tunis, where they were to film on location, Daniels first saw him as a grand figure whose limousine drove right up to the plane. However, in the course of seeing much of them over the next weeks, he found Guinness extraordinarily approachable while Merula was "a living saint". Guinness worried over whether the young actor was being paid proper expenses and offered to advance him some. They spent two or three weeks on desert location on some salt flats in windy and grotesquely hot weather on a hotel diet of unremitting veal or chicken - at one point the Guinnesses went down with food poisoning while there were often long frustrating waits while the ailing special effects had to be sorted out.

Incarcerated in metal, at one time having to lose an arm (torn off in a fight), Daniels found the waiting horribly painful, while he was generally rather embarrassed about the whole restriction of being a robot. Guinness helped his confidence greatly, he was especially clever at indirectly paying him compliments, while his calm and interest permeated everyone, including Mark Hamill who played Luke Skywalker. The image Lucas had of Guinness was of him sitting in a chair with a relaxed, approachable elegance, as if on the deck of a ship on some exotic cruise floating down a celluloid river. As for Guinness, Lucas in his total concentration reminded him of the young David Lean. But unlike Lean, Lucas did not dictate or impose. During the actual filming he had little to say although able to sense when Guinness was uncomfortable and walk across and "drop a brief word in your ear". Others found him not all that interested in the actors as such: "Very retiring, he doesn't enjoy directing actors very much. He would invariably say, after a take, "Terrific; can you do it again a bit faster?"

The heat and the waiting while they tampered with the machines was too much for Daniels but grimly he stuck it out: then, "One day Alec blew up ... Gosh I'm not wrong." thought C3PO. Guinness quickly returned to serenity: "a whirlpool of serenity" was the phrase Daniels used. During the laser/sword fight between Guinness and another actor his assailant lost concentration and failed to keep to the pre-arranged numbers with the result that Guinness "hit the wall and the floor. They ran towards him, He was all right but everyone was shocked. It was the fact he didn't lose his temper made me realise how angry he was."

"His presence," said Lucas, "lent so much credibility that everyone finally believed that giant furry aliens and talking robots made perfect sense." It was even more than a presence, however. Familiarity breeds contempt. The machines such as R2D2 ("Reel Two Dialogue Two") and C3P0, ("an euphonic accessory"), as well as the hirsute monsters, were often treated as they looked, or relegated to a sub-human plane and ignored. But Guinness would enter this world of weird creatures and adapt entirely to it, yet he remained well-centred in himself, and kept exactly within his own brief. As such he helped the cast and the production team to treat the menagerie as real, sentient beings. He brought to Star Wars and its two sequels (both written by Lucas but directed by others) in which Kenobi returns as a ghost (or as an underlying deity of "The Force"), its human identity and at a profound level helped the film to communicate its sense of the good (conceived of as an energy source) triumphing over the bad.

During the filming on location Merula, Guinness's own saint, would be all this time out sketching in the local town or market: on one occasion she was drawing a mosque when some of the gendarmerie stopped her, threatened arrest, and wanted to confiscate her sketchbook. She gave them a few pages, but kept her own drawings tucked away.

One moment during the filming was of special significance to the director. In the cockpit of Han Solo's spaceship where the area was cramped, and when Han was at the controls - with Chewie, the giant furry alien, next to him, and Luke and Ben standing squeezed in behind them - they played a scene during which Chewie had to reach up and hit a switch above Kenobi's head. In one of the takes Chewie reached up to flip the switch above Kenobi's head. In one of the takes Chewie reached up to flip the switch for the "umpteenth time and accidentally hit Alec right square in the face."

He was unhurt but taken completely by surprise, so he fell out of character. When Lucas looked at the film the next day in the editing machine he noticed that when he took the film from the moment Guinness was hit and studied it one image at a time he saw Guinness's face go through a series of different characters, "all in a split second, starting with Ben and ending with Alec, with about a half-dozen completely different characters in between".

Lucas then came to understand more clearly what he called:

An incredible physical nature of creating a character; how a truly gifted a character; how a truly gifted actor is so concentrated, so thorough that even their facial muscles are transformed. Like a chameleon, Alec has a lot of different shades, different colours and different characters. Every frame of film from the moment he was hit was a different character ... until he finally arrived at Alec Guinness.