There are many different types of public company, but to meet the basis criteria, any person who can come up with the $ for at least one share has the right to buy in.
The largest cos have literally millions of retail (i.e. people) shareholders, ranging from tiny investors of modest means to the very wealthy. However in recent times huge chunks of shares are often controlled by private equity funds (usually but not always the rich), mutual funds (again often small investors) and, PENSION funds (often theoretically 'owned' by small pensioners).
In most jurisdictions if one investor (group) gets >90% control, they can squeeze out the small shareholders and take the firm private (a periodic cause of litigation).
In some areas (i.e. Canada) there are different classes of stock. While the small shareholders share in the profits, only the controlling family gets to vote with their 'special' shares (i.e. Canadian Tire).