Amancio Ortega, the founder of the fast-fashion empire Inditex, could have never predicted the success of his Spanish fashion empire when he opened the first Zara store in 1975. Fast-forward 40 years later and Ortega is poised to surpassed Microsoft co-founder, billionaire Bill Gates in the Forbes Fortune 500 as the richest man in the world within the next two years - quite an achievement for a man who first began his career in the fashion industry selling quilted bathrobes.

From robes to riches: Zara founder to become world's richest man by 2017

Taking a closer look at the Fortune 500 list, it becomes apparent why Ortega is forecasted to overtake Gates as the number one billionaire as he remains the only billionaire on the list to have increased his value over the past six years, whereas Gates, US investor Warren Buffett - who Ortega surpassed this June as the second-richest man - and Mexican telecommunications tycoon Carlos Slim, have all been faced with a temporary downfall. Ortega's net worth grew a whopping 352.5 percent over the past six years from 18,3 billion dollars to 64,5 billions dollars to March 2015, whereas Gates, Slim and Buffett only managed to double their net worth.

Following Inditex's latest financial results for the first half of 2015 to July 31, 2015, which revealed a 17 percent increase in revenue to 10,6 billion dollars, Ortega's own net worth grew a cool 3,7 billion dollars. As of September 18, the Fortune 500 shows a 3,9 billion dollar difference between Ortega and Gates. However, FashionUnited business intelligence predicts that Ortega's overall net worth will continue to grow and hold steady at 71,5 billion dollars by 2016. Gates fortune, in comparison, is predicted to hold steady at 79 billion dollars and both Buffett and Slim will witness their net worths decrease 10 percent and 5 percent respectively. Ortega is set to overtake Gates by the second quarter of 2017, with an estimated value of 82 billion dollars.

Ortega's 'fast-fashion' business model set to make him the next #1 billionaire

Ortega's ongoing success is driven by the continuous demand for Inditex's trend-led brands, namely Zara, which undoubtedly helped the company increased its net worth from 36 billion dollars in 2010 to an all time high of just over 111 billion dollars. Inditex worth currently remains stable around the 100 billion dollar market to this date, which means that the company has increased 420.8 percent over the past five years and quadrupled its market value. This astounding growth is another reason behind Ortega's speedy climb to the top of the Forbes Fortune 500 list, as Gate's Microsoft has only increased 211 percent in the comparison over the same period.

Inditex's notably impressive achievements rest on a formula spun by Ortega which achieves continuous growth whilst holding onto the same margin on sales. Roughly 15 percent of Inditex's yearly revenue is available for investments, which is evident in the company's latest financial results. Inditex has opened 94 stores, creating over 10,000 jobs whilst expanding their online presence in Asia and Scandinavia over the past six months alone. As Inditex continues to focus on expanding its overall physical store space and turns its focus to strengthening its online market in China, Japan and South Korea, it is becomes clear that there is nothing standing in Ortega's way of surpassing Gates as the richest man in the world.

This is the first installation of a new series based on FashionUnited's unique business intelligence Top 100 Index. Stay tuned next week's installment on September 25th, which looks at the world's top sportswear brands Nike, Adidas and Under Armour