Who knows?

Einstein was once asked what it was like to be the smartest man alive, to which he replied "I don't know, ask Tesla".

Some have a false memory of his name being spelt "Nikolai" whereas all references today show "Nikola".

Best known for his design of the AC electricity supply system, Tesla became largely forgotten after his death in 1943. However, from the 60's onwards science had advanced sufficiently to enable his true genius to be much better understood, and the realisation of how far ahead of his time he actually was. 

The alternative memory some have of his first name probably comes from the popular misconception that he was Russian, where the name would be spelt that way. In fact Tesla was Serbian-American.

AC Electricity

The story of why we use AC electricity today goes directly back to Tesla. He was born in Austria as a Serbo-Croatian and later became an American citizen. His mother was particularly good at two things - fashioning tools and equipment mechanically, and having an extraordinarily good memory. Tesla later claimed her genes were the reason for his abilities. His invention of AC electricity was described as the greatest invention since the telephone.

Tesla's friend said if him:

Seldom did one meet a scientist or engineer who was also a poet, a philosopher, an appreciator of fine music, a linguist, and a connoisseur of food and drink.

-- Julian Hawthorne

He has a significant legacy on today's world. Many enterprises are named after him, the famous American electric car company, an SI Unit of Measurement, a minor planet (2244 Tesla) and he even has a day internationally recognised as a holiday, the 10th July, after him.

To Westerners used to only hearing his first name and unfamiliar with its spelling, Tesla's first name could pass as either Nikolai or Nikola. This Mandela Effect isn't about them, is the group of people who did pay attention and are sure it used to be Nikolai. The spelling of Nikolai is not arbitrary - it's an East Slavic version of what Westerners will know of as Nicholas and might be the one they've casually encountered, or it's variation, Nikolay.