The subatomic particle that carries a positive electric charge in an atom's nucleus is the proton. Each proton has a charge of +1 elementary charge, while its mass is about 1,836 times that of an electron.
Protons are found in the nucleus alongside neutrons, which have no net electric charge. The number of protons defines an element's atomic number: hydrogen has one proton, helium has two, and carbon has six. Changing the proton count changes the element itself.
The proton was identified through Ernest Rutherford's nuclear experiments in the early 20th century, although positively charged hydrogen ions had been observed earlier. It is not an elementary particle; it is a composite baryon made of two up quarks and one down quark, held together by gluons.
A common mix-up is confusing protons with electrons. Electrons carry negative charge and occupy regions around the nucleus, while protons remain in the nucleus. In a neutral atom, equal numbers of protons and electrons cancel electrically.