Final answer:
The Austrian composer who is most well known for his over 400 waltzes is Johann Strauss II.
Step-by-step explanation:
The correct answer is Johann Strauss II.
Johann Strauss II, also known as the Waltz King, was an Austrian composer who was famous for his waltzes. He composed over 400 waltzes, including the popular ones like 'The Blue Danube' and 'Tales from the Vienna Woods.' His music was highly influential during the Romantic era and is still loved and performed today.