The president is the person officially in charge — whether it’s of a republic, a company, a college, or a fan club.
This is a word for a leader, like the President of the United States or the president of the National Football League Players' Union. Many organizations have presidents, and they're usually elected by members of that group. When it’s followed by a name, the title president gets a capital p, as in President Obama. Whether with a P or p, the job of a president is to preside in a formal or official capacity.