What is an example of a freemium game?

Could you please provide me with an illustrative example of a freemium game? I'm interested in understanding how this model works in practice, and how developers are able to monetize their creations without charging an upfront fee. Is there a popular game that has successfully implemented the freemium model, and if so, could you explain how it does so? I'm eager to learn more about this unique approach to game development and monetization.