The reader needs to know this and it is your job as the writer to paint the appropriate picture for them.
To do this, it is a good idea to provide the reader with five or six relevant facts about the life (in general) or event (in particular) you believe most clearly illustrates your point. The importance of this step cannot be understated (although it clearly can be underlined); this is, after all, the whole reason you are providing the example in the first place.
For proof of this, consider examples from both science and everyday experience.
Because this is the first paragraph of your essay it is your opportunity to give the reader the best first impression possible.
Following the thesis, you should provide a mini-outline which previews the examples you will use to support your thesis in the rest of the essay.
Not only does this tell the reader what to expect in the paragraphs to come but it also gives them a clearer understanding of what the essay is about.
You see, if your essay has the same structure as every other one, any reader should be able to quickly and easily find the information most relevant to them.
The principle purpose of the introduction is to present your position (this is also known as the "thesis" or "argument") on the issue at hand but effective introductory paragraphs are so much more than that.
A one sentence body paragraph that simply cites the example of "George Washington" or "Le Bron James" is not enough, however.
No, following this an effective essay will follow up on this topic sentence by explaining to the reader, in detail, who or what an example is and, more importantly, why that example is relevant. For example, George Washington’s life was extremely complex – by using him as an example, do you intend to refer to his honesty, bravery, or maybe even his wooden teeth?