That's a measure of fame.
When nobody knows you, they use the complete name, Elon Musk.
When you're famous, they drop the given name, you're Musk.
When you're ultrafamous, they only use the given name, now you're Elon.
When nobody knows you, they use the complete name, Elon Musk.
When you're famous, they drop the given name, you're Musk.
When you're ultrafamous, they only use the given name, now you're Elon.