The positron is the anti-particle of the electron. Alternatively known as an anti-electron, it has the same properties as the electron with the exception of electric charge – the electron has a negative charge while the positron has a positive charge. The combination of an electron and a positron results in an annihilation which transforms both particles into high-energy photons.
Although the existence of the positron was predicted by Paul Dirac in 1928, the particle itself was not actually observed until 1932 (by Carl Anderson). It was the first example of a particle predicted to exist by quantum mechanics that was later discovered to actually exist. It has since been shown that all particles are associated with anti-particles.