I do not see how Guru Nanak "founded" Sikhism
Nanak is the first of the ten Sikh gurus, but that does not mean that he founded it.  As the word is usually understood, founding a religion means separating it from the other ones, and Nanak definitely never separated his followers from Muslims or Hindus.  In fact, many of Nanak's practices were things that were eventually forbidden once Sikhism was founded - for example, fasting and going on pilgrimages.  I believe that it was the last Guru who separated Sikhism from Islam and Hinduism.