Final answer:
Jorge Luis Borges is the Argentine writer known for introducing Ultraismo, a literary movement that was part of the early 20th-century modernist wave in literature.
Step-by-step explanation:
The Argentine writer known for introducing Ultraismo was actually Jorge Luis Borges, who isn't mentioned in the provided information. Ultraismo was a literary movement that emerged in Spain and Latin America in the early 20th century, emphasizing avant-garde aesthetics and pushing for a break with the traditional forms of poetry, specifically the influence of modernismo. Jorge Luis Borges, celebrated for his complex narratives and baroque prose, was significant in bringing this movement to the forefront in Argentina. Borges is seen as a key figure in Spanish-language literature and played a major role in this innovative movement, which became an important stage in the development of modernist literature in Latin America.