"In spite of great success, I think he's been under-rated," he said. "I thought he was the most important living painter in this country."
Emerging in the 1960s alongside David Hockney and Peter Blake, Caulfield became known for a distinctive style of planes of colour bound by strong black lines, creating stylised still lifes and interiors. His mature work also incorporated trompe l'oeil effects and photo-realism.
He was born in London in 1936 and spent the war years in Lancashire, then returned to the capital. Before his National Service he had worked in an advertising company painting chocolates, and he began night-school art classes while in the RAF.
Afterwards he won a place to study as a commercial painter at the Chelsea School of Art, before switching to fine art. He continued his studies at the Royal College of Art in the year below Hockney and RB Kitaj, and came to prominence as an artist in the hugely influential New Generation exhibition at the Whitechapel Art Gallery in London in 1964.
This helped to cement his reputation as one of the Pop Artists, although Caulfield himself always resisted being identified with any movement. Known as a painter and a print-maker, his work was collected by institutions around the world, from the Tate in London to the National Gallery of Australia in Canberra. His work was also seen in exhibitions such as those at the Walker Art Gallery, Liverpool, and the Tate Gallery in 1981, Arnolfini gallery, Bristol, in 1983, and the Serpentine Gallery, London, in 1992-93. A retrospective was held at the Hayward Gallery, London, six years ago.
But he also enjoyed commissions such as the design for a stained-glass window at the Ivy restaurant in London in the 1990s and a large carpet for the atrium of the British Council building in Manchester. He designed posters, book covers and ceramics, as well as sets for ballets, including Sir Frederick Ashton's penultimate work, Rhapsody, in 1995, and Michael Corder's ballet, Party Game, a decade earlier.
Caulfield, who continued to live in London, was nominated for the Turner Prize in 1987, but was beaten by Richard Deacon, and won the Jerwood Painting Prize in 1995 jointly with Maggi Hambling.
Sir Nicholas Serota, director of the Tate, said: "Patrick Caulfield was one of the most original image-makers in a talented generation of British artists. His still lifes and interiors capture mood and decor with incisive style."
Sir Howard Hodgkin admired his friend as "an exemplary Classicist". He said: "He was a very emotional person, but he turned his feelings into something very disciplined, very severe and elegant. He was wonderful company, very ebullient, cheerful and [also] melancholy. Not only was he a great friend but he was somebody I admired tremendously."
Leslie Waddington, his dealer of long standing, added: "I completely respected him both as a human being and as an artist. He was one of the outstanding artists of his generation anywhere in the world."
Although Caulfield had been working since his last exhibition at the Waddington Galleries, London, a couple of years ago, he had been ill for a while. He died on Thursday evening. He is survived by his second wife, Janet, and three sons by his first marriage.