Matte paintings are paintings that produce the illusion of a background or part of a background in film. They can also form part of a foreground.
Matte paintings are almost as old as movies themselves, and were originally painted on glass, and positioned in front of, and/or behind the actors (or stop motion creatures), creating the illusion in the camera of a complete scene.
Modern matte painting is composited, and usually created, digitally.
Tim Warnock is both a matte painter and a concept artist, and some time ago retired his paintbrushes in favor of a Wacom stylus.
I wrote a brief post about Tim Warnock back in 2005; since then his online portfolio has been redone and, of course, there is much new work.
His portfolio is divided between matte painting (image above, top and detail, bottom left) and concept art (above, middle and detail, bottom, right).
Warnock brings a talent for crisp realism, characteristic of matte painting, to his concept art. In both cases he uses sharp value contrasts and carefully controlled color relationships to give his scenes high definition and visual drama.