All kinds of instruments including the violin, cello, viola and if you consider your voice an instrument, a few choral pieces.
Dvorak was skillful composer of the Romantic Era, and wrote quite a bit of music he will be remembered for. One of his symphonies, the Symphony #9 in E Minor is commonly called the "New World" symphony, having been written in the United States. Some old editions of his works number this symphony as #5 but it is properly #9.
The "mystery composer" you are asking about is Johannes Brahms, although it is stretching a point to say that Brahms took older forms and styles and redefined them in a "modern" way.
Brahms certainly had his own voice, but no musicologist I have ever heard of would describe Brahms as an "innovator". He used existing forms in fresh ways, yes - but that's originality, not innovation - they are two different things. Brahms was a fine composer, but he was no trailblazer. His First symphony - and it is magnificent - was called "Beethoven's Tenth" for a reason.
Dvorak's most famous symphony is No. 9, "From the New World."
Dvorak was inspired by all of the folk melodies he heard in his native Bohemia, and they regularly show up in his compositions.
Antonin Dvorak spoke Czech, German, and possibly some English.
Antonin Dvorak was a Czechoslovakian composer, and was known for his folksy compositions. In modern terms, he would be considered a classical composer.
Why did Antonin Dvorak write "Largo" from the New World Symphony?
from the new world
Dvořák was from Bohemia, born near Prague in the Austrian Empire. He lived in Prague for most of his life, although he traveled to London multiple times and lived in New York from 1892-1895.