A small, stooped, grey figure stands absorbed by his own reflection in a mirror at the gallery's edge. It's as if he's trying to reassure himself he exists. As observers, we can only watch, fascinated and excluded by this alienating act. For the sculptor, Juan Muñoz, philosophical questions about the nature of the self, time and slippages between fact and fiction run through his diverse works.
Muñoz was the most significant sculptor to emerge from Spain after Franco's death in 1975, though much of his artistic education was actually acquired in New York and London, where, for a time, he worked as a dishwasher. Best known for his powerful dystopian cityscape Double Bind, created for the Tate's Turbine Hall in 2001, Muñoz had just begun a sculptural career when it was brought to an end by his death at the age of 48, that same year. Double Bind, with its false floors, its ambiguous levels and its shadowy grey men who seemed at once boringly bureaucratic and redolent of malice, was the high point of his short but substantial life as a sculptor.
It was an appropriate swansong for Muñoz, whose work was always concerned with architecture and the illusions of space. Details such as lifts or handrails litter the gallery. Lilliputian metal staircases lead nowhere, while typically Spanish balconies are set high on the gallery wall beside a metal sign that reads "Hotel": this is one that manifestly has no rooms and no guests.
Muñoz was significant among his generation of sculptors, who tended to be concerned predominantly with the language of art and materials. Although never interested in "representational" art, he happily reintroduced the human figure to act as both cipher and philosophical sign. He was as much influenced by the literature of Joseph Conrad, Günter Grass and T S Eliot as he was by Velázquez, Picasso, Francis Bacon, Robert Smithson or Thomas Schütte.
Theatre was also an abiding influence, particularly the work of Samuel Beckett and Pirandello. In his Raincoat Drawings, he created large chalk images of rooms, often formally furnished, that look like storyboards for old Hollywood films. All are devoid of human presence. A squashed sofa cushion, a door half open into a long, lit hall - they evoke the absence of people who only moments earlier had inhabited these spaces.
Like Pirandello's famous characters in search of an author, these are locations in search of characters. Rooms become stage sets in which the Beckett-like failures of human life are played out. The silence becomes an existential hell arising from the impossibility of speech and meaning. Muñoz's series of drawings of disembodied mouths evokes Beckett's Not I - in which just a mouth, illuminated by a single beam of light, speaks but says nothing - as well as the silent screams of Bacon's popes.
Acrobats, shop mannequins, ballerinas without legs, dwarfs and ventriloquists' dummies provided Muñoz with his cast of characters: outsiders all, rendered mute or impotent in this Borgesian game of life. The dwarf, influenced by the Infanta Margarita's young maid of honour in Velázquez's Las Meninas, is a constant figure. It not only recalls the protagonist of Grass's The Tin Drum, but the jester, the fool and the savant of Shakespeare.
In The Wasteland (the title is taken from Eliot's poem), a tiny ventriloquist's dummy sits on a metal shelf above a floor covered in a sea of complex marquetry. He looks as if he is waiting for his master to come and give him a voice - a master whom we, with our modern sensibilities, know is no more likely to come than the one for whom Godot's Estragon and Vladimir wait. In The Prompter (1988), a male dwarf made of papier mâché stands in a box in front of an empty stage of black and white geometric tiles, which create an optical illusion reminiscent of the floors of great baroque houses. At the far end is a drum. If we peer into the prompter's box we see that not only does the dwarf have no eyes, but he possesses no text. Drum and prompter alike are mute, the drum waiting for a drummer, the prompter waiting for actors or a script.
Both these works reflect Beckett's sentiments that human beings have the urge and imperative to express thoughts and emotions but struggle to find the means. The same idea is played out in the large group of not quite life-size Chinese figures, all of whom gesture and beam the same enigmatic smile, frozen as the timeless characters on Keats's celebrated Grecian urn.
Muñoz died suddenly on 28 August 2001, just months after the installation in the Tate of Double Bind. Without his existential and humanistic vision, the contemporary art world seems just that bit more glib and self-satisfied. Who knows what he would have gone on to make if he had reached his full maturity? But here was an artist unafraid of the big questions, of what it means to strive to remain an individual in this complex, modern world.
"Juan Muñoz: a Retrospective" is at Tate Modern, London SE1, until 27 April. For more information, visit: www.tate.org.uk