The answers to the questions are:
- The Pythagorean Theorem is named after: \( \boxed{\text{Pythagoras}} \)
- The longest side of a right triangle is: \( \boxed{\text{hypotenuse}} \)
- In the equation \( a^2 + b^2 = c^2 \), \( c \) represents: \( \boxed{\text{length of the hypotenuse}} \)