Juan Bautista Lázaro de Diego (León, 1849[1] - Ciempozuelos, 1919)[2] was a Spanish architect,[3] born to jurist José Benito Lázaro and astorgana María de Diego Pinillos.

[3] He received a gold medal in the National Exhibition of Fine Arts of 1897 and the Great Cross of Isabella the Catholic in 1901.

[6] He developed a remarkable activity in the restoration of architectural heritage in the late nineteenth century.

[7] One of his biggest contributions was the introduction of Catalan vault system in Madrid,[7] after travelling to Barcelona in 1888.

[3] Some of his works are: In his last years he developed a mental illness,[18] that led him to be interned in the psychiatric sanatorium of San José de Ciempozuelos in 1908, confinement that would last until his death in 1919.