People have known about electricity and magnetism for many centuries. 

The ancient Greeks noted that pieces of amber would attract light objects upon being rubbed.  That observation is responsible for the name electricity itself, since in Greek amber is elektron (ηλεκτρσνισ).

Magnetism was also known centuries ago.  The ancient Greeks knew that certain minerals attracted iron and other pieces of the same mineral.  About a thousand years ago, the Chinese noticed that a magnetised needle always points in the same direction and thus, can be used for navigation.

In time, people recognised that there are in fact two types of electric charges: positive and negative (after Benjamin Franklin (1706-1790)), and that opposite charges attract each other, while like charges repel each other.  In the 20th Century, Robert Millikan showed that the electric charge is quantized: that is to say, all electric charges are multiples of  an elementary electric charge found on the electron.

However, unlike electric charges which can be isolated, magnetic materials always have two poles (called North and South, after the directions they point towards on Earth).  If one breaks a compass needle into two pieces, each will again have both north and south poles.  It was apparently impossible to isolate a single magnetic pole.  Only the combination of north and south poles (called a dipole) seems to exist.

The absence of a single magnetic charge (called a monopole) implies the laws of electricity and magnetism are different, and this lack of symmetry has bothered physicists for years.