The correct answer is Francesco Petrarch.
He was one of the first people to actively start using the sonnet form, although he wasn't the one who invented it. Petrarch was an Italian poet, and his sonnets served as the inspiration for many other poets, such as Shakespeare, Sidney, Blake, etc. However, their sonnets differed - Italian sonnets that Petrarch wrote didn't have the same structure as English sonnets that Shakespeare or Spenser wrote.
