It was established in the Constitution Article 2, Section 1
The process was changed in the 12th Amendment.
The founders were leery of pure democracy and felt that direct election of the president by popular vote would wind up with populist presidents who were beholden to the ever-changing winds of popular opinion instead of reasoned leadership. The alternatives debated was having the state legislatures choose a president or the Congress but they then felt that the president would then be too beholden to the states or Congress respectively. So they eventually settled on letting the states choose how to choose the president with the electoral college as a method to add a layer of separation.
The states subsequently moved as close as they could in this system to a popular election of the president and we are seeing just the effects from that the founders feared.
Thank you for the source material. We live by the Constitution so we need to go by this. Is there a process whereby one makes it known that he is willing to be the President or can the vote be for any citizen who meets the qualifications for President? I don't think this is saying a person who "runs for President" needs to have a running mate.