Gold has been used as a currency historically for many reasons. It's inert. It has a low melting point. It's malleable and easily divisible. It doesn't tarnish. A piece of gold from 2,000 years ago will be the same weight today as it was then. It also is attractive, which gives it value for jewelry. And, importantly, it's predictably rare and can be mined.
Today, it's also valuable for electronics. Its inability to tarnish makes it fantastic if you need a connection to be corrosion resistant.
There's a reason gold still holds its value even though it's not used for currency anymore.