Hi Lauren,
I think to say that the magnetic field controls the planets might be a bit strong, but it certainly effects them.
Magnetic fields were first discovered on the Sun around 1907-1908 by George Hale who measured the magnetic field in sunspots at Mt. Wilson Observatory (see
http://physics1.usc.edu/solar/history.html). Understanding how the solar magnetic field and related things like the solar wind, flares, and coronal mass ejections effect Earth and other planets has been a long journey, though, and we are still working on it.
best,
Terry