Architect Louis Kahn was an American architect who is widely regarded as one of the most influential architects of the 20th century. He is best known for his use of exposed brick and monumental structures, such as the Salk Institute in California and the National Assembly Building in Bangladesh. His work has been described as 'poetic modernism' and he is remembered for his unique approach to design. The answer to the crossword puzzle is KAHN, which is the surname of this renowned architect.