Hassler (also Haßler, Häßler, Hässler, Hasler, ...) is a toponymic surname derived from a number of places called Hasel or Hassel in German-speaking parts of Europe. Notable people with this name include: Musicians. A musical dynasty in Nuremberg. Isaak Hassler (c.1530 – 1591), organist and father of three brothers: Kasper Hassler (1562–1618), minor composer and publisher. Hans Leo Hassler (1564–1612), an important German composer and organist. Jakob Hassler (1569–1622), composer most noted for his keyboard works. Johann Wilhelm Hässler (1747–1822), German organist and composer. Athletes.
https://en.wikipedia.org/wiki/Hassler