The first tweet was sent by Elon Musk.
Why it is true
The first tweet was sent by Jack Dorsey, co-founder of Twitter, on 21 March 2006. It said just setting up my twttr. Elon Musk only bought the platform in 2022.
Source: Twitter
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.