A monopolist is an individual, business, or entity that holds a dominant share of the market in relation to its competitors and has enough power to set market prices. When a company or individual is the monopolist, they are the sole producer or seller in the marketplace and there are no meaningful substitutes. As such, they can take advantage of their monopoly power to charge consumers high prices and in turn, earn higher profits than companies in more competitive markets.

In many cases, governments have stepped in to control monopolies by passing antitrust laws. These laws seek to protect consumers from unfair business practices, ensure access to a variety of goods and services, and limit the power of a single entity to control a significant portion of the market share. However, there are some legal monopolies that are sanctioned by the government, such as companies in the utilities sector.

Monopolists take advantage of their market dominance to increase profits, but it can often be difficult for new companies to enter the market due to the steep entrance and operating costs. Moreover, the monopoly power allows the monopolist to block product innovations and benefit from stagnant prices, creating a stifling effect on competition and consumer choice.

In conclusion, while monopolies can produce some benefits such as lower costs and high quality services, they can also lead to high prices, reduce competition, and limit consumer choice. Therefore, governments must regulate monopolies and enact competition policies to ensure that businesses don't abuse their monopoly power and limit the open market.