The strange ego of Mark Wallinger

He has dressed in a bear suit, built a brick wall, and in his new show at the Baltic he has a bizarre self-portrait. The artist explains why to Hannah Duguid

A series of self-portraits by the artist Mark Wallinger are on show at the Baltic Centre for Contemporary Art in Gateshead.

The portraits consist only of the letter "I", as a capital or small letter, in different fonts and handwritten. It is "I" as a self-portrait. The letter represents the self and also has the vertical form of a human figure. It is witty and absurd, a self-portrait which effaces individuality with a universal representation of it. A big or small "I" might equate to a big or small ego. At Baltic, Self Portrait (Times New Roman) is 20 metres high. As Wallinger says: "Depending on one's mood one might be more receptive to one 'i' or another, sometimes one might feel like the dictator of a small state and other times you might feel like a very vulnerable and put-upon human being. In the Times New Roman font, it is a pillar in its symmetry and singularity, and the shape of a person. The sculptural version is my height, and I stood it on a plinth to give myself a bit of status." And he laughs, which dissolves any sense that he might take the idea of his status very seriously.

In person he is affable, with a light easy charm. Wearing large black glasses and a dark loose blazer, he has the appearance of a well-turned-out academic. He speaks thoughtfully, taking time to find the right words, which still bear traces of an accent from his Essex childhood. He moved to London in the 1980s to attend Chelsea Art School, and then Goldsmiths college.

At 53, he could be described as one of our more senior artists; he has ticked off the important awards, winning the Turner Prize in 2007, and representing Britain at the Venice Biennale in 2001.

Wallinger has been working as an artist for 30 years, but he remains difficult to define. His work has taken a variety of forms: from Sleeper which was a performance in a bear suit at Berlin's Neue Nationalgalerie, to a replica of Brian Haw's war protest shown at Tate Britain, to Race, Class, Sex which are sensual and beautiful paintings of racehorses, and Ecce Homo, a pale figure of Christ wearing a barbed-wire crown which stood on the fourth plinth in Trafalgar square in 1999.

"I like to think that my interests and preoccupations range fairly widely, and I think as an artist one should, kind of, be an explorer. I don't think I was a person who wanted to light upon a signature style and then hone that. There's a temptation to being an artist as a small business but I don't really turn out commodities as such," he says.

Two new works are vast numerical installations, which are so overwhelming in scale that conceptually they are difficult to grasp. There are 16 zeros in a work titled 10000000000000000. It consists of a giant checkerboard made from 1,024 chess mats with 65, 536 squares covered in 65,536 individually numbered stones. Like his self-portraits, the individual and the universal play out as themes in this work. "It is showing what is ungraspable, and the infinite variety in something as banal as a stone, which when they are placed in this way become sort of jewel-like. Each one is considered in its entirety, and it shows the teeming, profuse nature of phenomena in the world, to try and both have that abundance and that absolute particularity," he says.

This idea continues through another new work titled The Other Wall, which is a brick wall made from 10,000 bricks individually numbered, and arranged randomly. There are ideas about chance and infinity inherent in the wall, as well as ideas about how it might relate to other walls, imagined or real, such as the Berlin wall. Wallinger likes the idea of using a humble brick as a material to create such complex ideas. It relates to his work MARK 2011, also on show, in which he wrote "MARK" in chalk on bricks all over London. The pun is in the idea of mark-making. Get it?

There is romanticism to the way he perceives his work, and the world. He suggests that the sublime, which used to be nature at its most awe-inspiring, might now be found in the overwhelming idea of cyberspace. His engagement with ideas seems limitless.

He is currently working on a project with the National Gallery and Royal Ballet – along with Chris Ofili and Conrad Shawcross. Metamorphosis: Titian 2012 draws on Titian's pictures based on Ovid's epic poem Metamorphoses. The multi-arts project will include sets and costumes designed by the artists and will open with a ballet performed in Trafalgar Square and broadcast live across the UK.

"It's a great project to work on," says Wallinger, "an unbelievable opportunity. I can't say too much as I want it to be a surprise when it opens but I have run with the theme of the moon goddess. So the set has lunar overtones. It's kind of black and white, monochromatic."

Wallinger's other large ongoing project is The White Horse, a design for a 50m-high white horse to stand in the Ebbsfleet valley in Kent. He has a romantic's love of horses and racing. "Very simply it's a horse in a field but people who know will recognise that the way he is standing goes back to Stubbs. It's about the confirmation of the thoroughbred, and it's a very staged pose for painters. But he's a white horse and has the associations with ancient white horses. He will stand where the North Downs meet the Thames, which is where the cement industry grew up, and where in Saxon mythology Hengist and Horsa arrived in Britain with the white horse as their standard. He will be some huge sentient being who can see so much further than we on the ground are able to see, which will be rather optimistic, I hope, because he can see further into the future than we can." Before he gets too carried away with this romance, he adds, "And it would be somewhere to go on a Sunday, which will be better than going to Bluewater shopping centre." This thought makes him laugh, again.

Ecce Homo was the artwork that made his name. His proposal for the Olympic games, titled O, was for 10 giant white spheres to mark the 10 gateways to the Olympic Park. It was, he wrote, "a symbol that encourages them [children] to dare, to dream". The proposal was rejected but there's no bitterness about this.

"Being an artist is kind of odd in that it's not like being a writer or being in a band where you can build a grass-roots audience and tour the country. Artists are still reliant on old-fashioned patronage, either from the state or from people who have enough disposable income. To be able to make public works appeals to something that's about a more direct relationship with an audience who don't have to go into a special gallery or museum," he says.

Such resistance to elitism perhaps reveals Wallinger's roots as an artist who made political work that challenged ideas about social class. "I think people gloss over how divisive the Eighties were and how the government was destroying a postwar consensus, and we're still living through the consequences of that. I spent 10 years being angry," he says.

His workload these days sounds overwhelming but he rebuffs any opportunity to let his ego, the big "I" in his self-portraits, take over. The main reason for pursuing his career as an artist was, he says: "I wanted to avoid getting a proper job. I couldn't bear a life having to do someone else's bidding. There's quite a lot of drudgery being an artist but it's my own drudgery." And with that, he laughs and then says: "At least it's all my own fault."

'Site', Baltic Centre for Contemporary Art, Gateshead (balticmill.com) to 14 October. 'Metamorphosis: Titian 2012', National Gallery, London WC2 (nationalgallery.org.uk) 11 July to 23 September