He was one of the first composers to add additional instruments to the Symphony orchestra.​

Haydn

Explanation:

Haydn also introduced the following innovations: trumpets were used independently instead of always doubling the horns, cellos became separated from the double basses, and woodwind instruments were often given the main melodic line.

composer Claudio Monteverdi

People have been putting instruments together in various combinations for millennia, but it wasn't un- til about 400 years ago that musicians started forming combinations that would eventually turn into the modern orchestra. Around 1600 in Italy, the composer Claudio Monteverdi changed that.

they are often in theme and variations