Sergei Rachmaninoff was a Russian composer, pianist, and conductor who is widely considered one of the greatest composers of the Romantic era. He composed a wide variety of works, including symphonies, operas, piano concertos, and chamber music. His works are known for their lush, romantic melodies and powerful orchestration. He was also a renowned pianist, performing his own works as well as those of other composers. He was highly influential in the development of 20th century music, and his works remain popular today.