The Cupertino, California company's shares added another 0.3 percent on Friday, putting its market capitalization at $1.005 trillion.
Given the volatility of the stock market, however, it's possible that Apple will not remain at the $1 trillion mark in the coming days.
Apple shares have been on a tear since Tuesday, when the tech giant reported strong 2018 fiscal third-quarter earnings.
With a closing price of $207.39 on Thursday, Apple became the first publicly listed US company to ever reach $1 trillion in market capitalization. The company's stock price started rising subsequently, resulting in 2.92 percent gain during the trading hours and closing at $207.39 in NY on Thursday. However, his net worth is tied to Apple stock in a less conspicuous way.
The landmark is the latest victory for Tim Cook, who faced scepticism when he took over as chief executive in 2011 from ailing iconic co-founder Steve Jobs.
That made Apple worth more than all but the 15 richest countries in the world, based on 2017 data from the CIA World Factbook (based on gross domestic product).
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As with other landmarks - such as the Dow crossing 25,000 points for the first time - the Apple record is significant because of its resonance beyond the financial universe.
Together with Facebook (FB.O), the five largest US companies account for 15 percent of the S&P 500.
"Steve (Jobs) founded Apple on the belief that the power of human creativity can solve even the biggest challenges - and that the people who are insane enough to think they can change the world are the ones who do".
Though many investors consider Apple a hardware company, Jackson said most consumers have a different relationship with Apple's products.
He ended the letter writing: "Just as Steve always did in moments like this, we should all look forward to Apple's bright future and the great work we'll do together".