Dirac was the first to purpose this type of monopole. He did this as an explanation for the quantization of charge. The existence of a Magnetic monopole would also make Maxwell's equations symmetric, something that is to be desired. The GUT ( Grand Unified Theory) Magnetic Monopoles also must exest but for a different reason. In GUT symetry is not a desired affect but a requierment for the theory to work. The difference in origion results in some suprisingly different properties. The Dirac monopole is a point source with elemenary "charge" three times greater than that of the eletric charge. It has mass larger than an electron but not orders of magnitude larger. GUT monopoles can have bothe eletric and magnetic charge. The also have a detectable radius and enormous, for particles, masses. There is some reason to wonder if monopoles could be black holes.