Einstein said that Nikola Tesla is who was the smartest person.
Albert Einstein reportedly jokingly said that Nikola Tesla was the smartest person when Albert Einstein was asked about his own intelligence.
Although there's no concrete evidence that says for sure if he did in fact say that.
The quote of "I don't know, you'll have to ask Nikola Tesla, "is often also attributed to him in this context, but it's also likely a fabricated story that has been passed around.
There are not sources that are reliable to prove that Albert Einstein said this, such as in diaries, letters or interviews which document that Albert Einstein said this about Nikolas Tesla.
Both Tesla and Einstein were brilliant scientists, but they didn't particularly admire each other's work, especially when it came to the topic of relativity.
The quote from Albert Einstein about Nikola Tesla being the smartest person also appears to have actually originated as a popular anecdote, and may have been potentially embellished over time.
It's a good story that does play on the idea of Albert Einstein's humility and Nikola Tesla's genius, but there's no historical basis to confirm it.