Unico Wilhelm van Wassenaer (1692-1766) was a Dutch aristocrat whose work as an amateur composer was only uncovered by musical scholars and researchers around 1980. Among his works are the 6 Concerti Armonici, or Harmonious Concertos, which were published in his lifetime without attribution, and were assumed to have been written by Pergolesi. The works are stunningly beautiful, and the Tarantella from the B-flat Major concerto was parodied by Stravinsky in his Pulcinella Suite.
On a personal note, my college harmony teacher, Ivan Tcherepnin, taught the Andante from the 1st G-Major concerto, and called it a "perfect piece of music." My favorite recording is the set by Camerata Bern, which CD is out of print, but is available on Amazon music, and on YouTube:
Concerto I in G Major
Grave (Camerata Bern)
Allegro (Camerata Bern)
Un poco andante (Camerata Bern)
Allegro (Camerata Bern)
Concerto 2 in B-flat Major
Concerto 3 in A Major
Concerto 4 in G Major
Concerto 5 in f Minor
Concerto 6 in E-flat Major