Guerra died Wednesday at his home in Santarcangelo di Romagna, in northern Italy, according to an announcement on the Tonino Guerra Cultural Assn. website.
"I think he's one of the greatest writers of our time whose medium happens to be the screenplay," said Howard A. Rodman, vice president of the Writers Guild of America, West and a professor at the School of Cinematic Arts at USC.
"He collaborated with many of the great filmmakers of his era ... and his work with them is in every case the groundbreaking and significant work we associate with them," said Rodman.
"When you think of European modernist cinema, the cinema that changed the way we think of movies, that inspired the glories of American cinema of the 1970s and cinema around the world, it's astonishing how many of those films were written by Tonino Guerra."
Among the scores of films he wrote or co-wrote are "La Notte," "L'Eclisse," "Red Desert" and "Zabriskie Point" for Antonioni, "Ginger and Fred" and "And the Ship Sails On" for Fellini, "Nostalghia" for Andrei Tarkovsky, "Landscape in the Mist" for Theo Angelopoulos, and "Illustrious Corpses" for Francesco Rosi.
In 2011, the frequently honored Guerra received the Writers Guild of America, West's Jean Renoir Award for Screenwriting Achievement. It is presented to an international writer who has advanced the literature of motion pictures and made outstanding contributions to the screenwriting profession.
The son of a fisherman/fishmonger father and an illiterate mother whom he later taught to read and write, Guerra was born March 16, 1920, in Santarcangelo di Romagna.
He began to orally compose dialect poems while imprisoned in a German concentration camp during World War II, and he published his first collection, "I Scarabocc" ("Scribblings"), in 1946.
After earning a degree at the University of Urbino with a thesis on dialect poetry, he taught secondary school before moving to Rome in 1953.
He launched his screenwriting career with director Giuseppe De Santis' 1956 film "Men and Wolves," co-written with Elio Petri.
His longtime collaboration with Antonioni began with "L'Avventura," the breakthrough 1960 film that brought international renown to the director, who co-wrote the script with Guerra and Elio Bartolini.
"Antonioni struck a chord in exploring people's sense of alienation in an increasingly industrialized and impersonal world," said film reviewer Kevin Thomas, a former Times staff writer. "Without question, Tonino Guerra was a major contributor to Antonioni's masterworks, a collaborator who enabled Antonioni to express his unique vision."
In the preface to his published screenplays, Antonioni said that he and Guerra "have long and violent arguments ... and that makes him all the more helpful."
Of his collaboration with Guerra, Angelopoulos once said: "Tonino has been my psychoanalyst for 20 years."
Guerra, who worked with American, Greek and Russian directors, said in a 1993 NPR interview that each filmmaker had made him aware of a different aspects of himself.
"Fellini is always immersed in his childhood, in his background, in his memories," he said. "Coming from Rimini, which is near my own hometown, he obliged me to look here locally, to look into my own memory, my own childhood.
"Tarkovsky, with his religious problems, his preoccupation with his spirituality, he raised all my own spiritual doubts. Rosi, with his attention to the meticulous detail of daily life, he made me think of what was happening, what was happening under my feet, in front of my eyes, every minimal detail."
Guerra's transition from poet to screenwriter was a natural one.
"My poems were an essence of images," he once said. "They had the cinema inside them before I started working for it."
Observed Rodman: "During the great flowering of European cinema after World War II, he was its poet and guiding light. I think he was able to figure out how to put in words and images many of the great themes and sensibilities of the world's best filmmakers."
Guerra is survived by his second wife, Lora; and his son, Andrea, a film and TV composer.