If you had to choose an actor to play Che Guevara, Gael García Bernal would be near the top of that list. As anyone who saw Y Tu Mama Tambien knows, he's got charisma to burn; as anyone who saw the 2003 Oscars knows, he's got the lefty politics. The Motorcycle Diaries is about a cross-continent trip the youthful Ernesto Guevara (played by Bernal; the "Che" name came later as a reference to his Argentinian origins) took with his companion Alberto Granado (Rodrigo de la Serna). The motorcycle of the title is a beat-up Norton 500, Ernesto and Alberto's tool in their 8-month journey from their Argentinian home to Caracas, but The Motorcycle Diaries is not really about the art of motorcycle maintenance, but the awakening of Guevara's social consciousness. (Indeed, the Norton, worn beyond repair from the strains of the journey, has to be abandoned at an early stage of the trip.) Together, pretending to be leprosy specialists, they criss-cross the continent, and the journey leaves the comfortably middle-class Guevara faced with incontrovertible evidence of the lack of progress among the native peoples, who are forced by economic circumstances to work in mines and whose every effort to organise is put down.

Walter Salles (who directed the wonderful Central Station) depicts visually the diversity of the South American continent, from the snow-covered Andes mountains to the coastal town of Valparaiso in Chile to the magnificent ruins of Machu Picchu, and the sharp contrast between the glory of the landscape and the ruination of the landscape's indigenous people. Small wonder, in the context of these vast geographic and social disparities, Guevara's lovelorn thoughts of his fiancee and the pair's flirtations with local women give way to the more serious thoughts of social equity.

Ultimately, what makes The Motorcycle Diaries succeed is its humanisation of Guevara. After all, Guevara was a man before he became Che the icon, reproduced on thousands of T-shirts for college kids, and there's no cheap irony about his future in the film. Instead, the slow transition from boy to man and the awakening of political conscience are shown to us. Initially, naively perhaps, the two men hold an enduring power in science and its capability for advancing people's lives; by the film's end, there's a strong sense that beyond science, beyond religion even, there is a realm in which people must take some sort of political action. But this is no soporific revolutionary tract. Throughout the movie Bernal radiates that easy charm that made Guevara so appealing. This is a Guevara who's generous of spirit, at ease with people from all walks of life, and full of fervour but still capable of laughing at his own stumbling efforts at dancing, and still capable of drunkenness, of joy at football games and at Granado's incredible luck at a game of blackjack, and of warmth and understanding of his friend's love of women.