Although Musk said on Twitter on Sunday morning that he "don't know" who is the CEO of Twitter, a signature document he just submitted to SEC to remove all the questions: it is Eron Musk himself. The public confirmation of is part of the 13th (and probably last) amendment of the first filing on April 4.

At that time, Musk acquired more than 9% of Twitter's available shares in a few months. Now, this document is updated for the 13th time (Musk is the "reporter" in the document):
This Schedule 13D amends Schedule 13D originally filed with the U.S. Securities and Exchange Commission on April 5, 2022, involving ordinary shares of Twitter, Inc., with a par value of $0.000005 per share ("common stock"). ("Issuer" or "Twitter"), followed by amendments on April 11, 2022, April 14, 2022, April 21, April 26, April 2022, April 27, April 2022, May 5, May 25, May 2022, June 6, July 8, 2022, August 30, September 9, 2022 and October 4, 2022 (including this revision, collectively referred to as "Schedule 13D"). Capital terms used but not defined herein have the meanings given to these terms in Schedule 13D.
document states that the "reporter" is the CEO (CEO) of the merged company.

Musk and his venture capitalist friends, as well as a small group of Tesla engineers who brought to Twitter are working together to fire executives and assign tasks to new engineers over the past few days. These tasks include some rather peculiar ideas, such as a closer look at the source code of Vine a decade ago and an attempt to build a premium verification service of $19.99 per month in a short period of time.
file also shows that Musk's "SMS Friend", Twitter co-founder and two former CEOs, Jack Dorsey, has transferred his shares to the new parent company.

Other private investors are on the list, including private offices like Saudi Arabia Holdings and Prince Alwaleid Ben Taral, which also owns stake in Twitter, which has spurred Senator Chris Murphy to ask the US Council on Foreign Investment (CFIUS) to conduct a national security review of the deal.