(CNN) -- Brazil's most influential modern architect Oscar Niemeyer, whose resume includes the United Nations building in New York, passed away on Wednesday.
He was 104.
Niemeyer spent the last month in a hospital in Rio de Janeiro in frail health, according to his doctor Fernando Gjorup. Neimeyer died after suffering respiratory complications, Gjorup told reporters.
Niemeyer was one of Brazil's geniuses, said Brazilian President Dilma Rousseff.
"We have to dream, or else things won't happen," Rousseff said, using one of Niemeyer's famous sayings. "Few have dreamed so intensely and accomplished so many things like him."
The president offered the presidential palace, one of Niemeyer's well known designs, to his wife for his wake.
Eduardo Paes, the mayor for Rio de Janeiro, has declared official mourning for three days.
"(He was) one of the greatest geniuses that Brazil gave the world, Oscar Niemeyer was more than a brilliant and innovative architect. He defied logic and twisted ways to create true works of art," Paes said.
Born and raised in Rio, Niemeyer was an early master of modern architecture in Brazil, a fingerprint that became clear after he was commissioned alongside his mentor Lucio Costa to design Brazil's new capital, Brasilia.
Niemeyer "incorporated curves and raw, unfinished materials" with a "balance between horizontal and vertical buildings, rectangular volumes," the United Nations Educational, Scientific and Cultural Organization said.
Brasilia is a World Heritage Site.
Among his other works are the presidential palace, the ministry of justice building and the presidential chapel.
In Rio, his sinuous curves inspired the works of many poets, writers and songwriters. He designed the Sambadrome, where the samba schools hold their parades every year. In Sao Paulo, he worked with a landscape architect to build one of the largest city parks in Latin America, the Ibirapuera Park.
Paes summed up what many felt when he said "Brazil and the world lost today a man who dedicated his entire life to produce beauty."