There are numerous versions of the story of William Tell, going back to the fifteenth century. Most of them, including Schiller's play William Tell, agree on certain basic facts, including the tyranny of Governor Gessler. Gessler sets his hat on top of a pole in front of the new prison he has built, and he commands everyone who passes by to bow to it, on pain of death.
Passing by, Tell fails to bow to the hat. In some versions of the story, William Tell openly defies this order, but in Schiller's version, Tell says that it was an oversight on his part. However, Gessler happens to be passing by as Tell is arrested. He has heard stories of Tell's reputation as a marksman. Gessler wishes to determine for himself whether these stories are true, and so he orders Tell to shoot an apple from his son's head. If he misses, he dies.
Gessler is represented as being genuinely curious about the reputation of William Tell and whether Tell will be able to live up to that reputation. This curiosity is natural enough, but his method of settling the matter is a testament to his perverse and tyrannical nature. When Tell has completed the task, leaving his son unharmed, Gessler remarks that he saw Tell place two arrows in his belt before shooting the apple with one of them. He asks what the other was for, whereupon Tell replies that if his son had been harmed, the second arrow would have gone through Gessler's heart. Upon hearing this, Gessler commands that Tell should be arrested after all.