Whether it's money, power, or fame, success means something different to everyone.

For Bill Gates, it's defined by two factors: making a difference and taking care of the people closest to you.

"Warren Buffett has always said the measure [of success] is whether the people close to you are happy and love you," Gates explained during a Reddit AMA, or "ask me anything," on Monday, when asked about his idea of success.

"It is also nice to feel like you made a difference — inventing something or raising kids or helping people in need," he continued.

Although his inner circle is harder to penetrate, it's easy to see that Gates has certainly accomplished the latter piece of his answer.

At just 20, Bill Gates cofounded Microsoft with his childhood friend Paul Allen. Months before his 31st birthday, the company went public, making Gates a billionaire.

Now the richest man in the world with $85.2 billion to his name, Gates spends his days running the Bill & Melinda Gates Foundation, one of the most powerful charities in the world. The foundation — which controls an endowment of more than $40 billion — aims to lift millions of people out of poverty, with a heavy focus on eliminating HIV, malaria, and other infectious diseases.