“There is nothing special about David Cerny’s art, other than that he is more visible than other artists and talented at marketing,” Mr. Knizak said. “But artists like Cerny who are in headlines today will be forgotten tomorrow. His work is destined for the amusement park and won’t stand the test of time.”

Mr. Knizak, whom Mr. Cerny once depicted inside the same towering sculpture of a rectum where he placed his other nemesis, Mr. Klaus, may not be the most objective critic.

In a 2003 work titled “Brown-nosers,” museumgoers were asked to climb a ladder and peer into a hole in the huge white rear end, where a video showed impersonators wearing rubber masks of Mr. Klaus and Mr. Knizak, feeding each other slop to the tune of “We Are the Champions.” Mr. Cerny is so contemptuous of Mr. Knizak, whom he accuses of fawning on the establishment, that he once refused to enter the National Gallery to accept an award. “It was hate at first sight,” he said.

Mr. Cerny first drew attention in May 1991, when, at 22, he was arrested after painting a giant Soviet tank pink, transforming a memorial to the liberation of Czechoslovakia by the Red Army in 1945 into the sculptural equivalent of a large pink toy.

Recalling his hooliganism, for which he spent a few days in prison, Mr. Cerny said the tank had been a symbol for him and his generation of the Soviet-led occupation of Czechoslovakia in 1968 and a monument to decades of Russian oppression. “I was sick and tired of passing by this tank, two years after Communism had fallen,” he said. “I was standing with a friend one day at a tram stop nearby staring at it and we both decided we should defile it.”

THE son of a painter and a restorer of 15th-century art, Mr. Cerny traces his impulse to revolt to a childhood under Communism, when freedom of expression was suppressed.

When he was 4 years old, a statue of Lenin was erected in a square near his house. One day, he and his father were driving by, and his father muttered, “They would be better off building streetlights.” When he repeated this at kindergarten, he said, the teacher called his parents to warn about their young subversive.