Bitcoin was envisaged by a pseudonym 'Satoshi Nakamoto' in 2009 as a pure peer-to-peer version of electronic cash would allow online payments to be sent directly from one party to another without going through a financial institution. It can be said that Bitcoin was to serve as a currency alternate to the government controlled money we use today.
So why is the identity of its creator important? It all boils down to the control over the price of Bitcoin.
Bitcoin is programmed to have a finite supply of 21M units which would be released over its lifetime through a process called bitcoin mining. In contrast to this, all the major fiat currencies can be printed at will by the central banks and governments (a few people) leading to flooding or sucking the markets of its liquidity.
Bitcoin has grown incredibly big over the years and its larger than the balance sheet of many of the countries' central banks. Bitcoin's market cap (including its offshoots Bitcoin Cash and Gold) currently stands at US$ 320B. The total US$ bills in circulation across the world is currently about US$ 1.5 Trillion.
Satoshi Nakamoto holds roughly 1M Bitcoins as of date (~ 5%) (Yes! and this is verifiable through the public ledger). To put things into perspective. Lets take the example of Gold : The US government holds 8000 tons of gold out of 187,000 tons of gold ever mined by humanity (~4.3%). So Nakamoto's stake in Bitcoin is more than the entire US government's control over gold.
Hence, Nakamoto possesses immense control over the price of Bitcoin. His decision to flush the market with his Bitcoin holding can crash the price and wipe billions of dollars of wealth.