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.
Despite the fact that, as Shakespeare said, "the pen is mightier than the sword," the pen itself is not enough to make an effective writer.
In fact, though we may all like to think of ourselves as the next Shakespeare, inspiration alone is not the key to effective essay writing.
The introductory paragraph not only gives the reader an idea of what you will talk about but also shows them how you will talk about it.
Put a disproportionate amount of effort into this – more than the 20% a simple calculation would suggest – and you will be rewarded accordingly.
Active voice, wherein the subjects direct actions rather than let the actions "happen to" them – "he scored a 97%" instead of "he was given a 97%" – is a much more powerful and attention-grabbing way to write.
At the same time, unless it is a personal narrative, avoid personal pronouns like I, My, or Me.
The famed American inventor rose to prominence in the late 19th century because of his successes, yes, but even he felt that these successes were the result of his many failures.
He did not succeed in his work on one of his most famous inventions, the lightbulb, on his first try nor even on his hundred and first try.