Late last month, Elon Musk completed his acquisition of Twitter and immediately fired four of the company’s most senior executives.

In their place, he’s installed a small council of lieutenants to assess the company and begin implementing his vision. The group includes Musk’s personal lawyer, his chief of staff, a couple investor friends and a former Twitter executive who left the company years ago.

The new regime has already started mass layoffs, discussed the company’s content moderation plans and sent out orders to employees to begin working on a paid verification feature. They also met with advertisers who provide Twitter with most of its revenue and have shown concern over how Musk might run the company.

They’re tasked with keeping the company going and ramping up its revenue.

Here’s a run-down of who they are.

Jason Calacanis

A tech investor, podcast host and longtime Musk associate, Calacanis’ texts with Musk were among those that appeared in court documents released as part of Twitter’s lawsuit to force Musk to buy the company. Calacanis pitched Musk ideas on how to change Twitter before the acquisition. And now that Musk is formally the owner, Calacanis has been on Twitter soliciting feedback from users on what kind of features they want to see.

In his private texts to Musk, Calacanis suggested that Twitter require employees return to the office for at least two days a week, which he said would reduce the workforce by 20 percent, through “voluntary departures.” He also criticized Twitter’s premium features and proposed expanding verified badges to more users, the messages show.

In private texts, he told Musk that becoming the new chief executive of Twitter is his “dream job.” He’s not CEO, but Musk has kept Calacanis around as part of the transition and his title is listed internally as a software engineer.

On Monday, Calacanis tweeted that he was in New York to meet with advertisers on behalf of Twitter.

Jared Birchall

Birchall is one of Musk’s closest advisers and manages the billionaire’s personal fortune as head of his family office since 2016. He’s a former Morgan Stanley wealth manager and helped set up the financing for Musk’s Twitter buyout.

Birchall also serves as chief executive of Neuralink, Musk’s brain interface tech start-up and as a director of his tunneling company, Boring Co., though it’s unclear if he actually wields power there or is simply in charge on paper. Birchall is Musk’s fixer, helping arrange the purchase and sale of his houses and the hiring of security guards.

Over the last few days, Birchall has been one of the people strategizing inside Twitter.

Alex Spiro

A lawyer at New York law firm Quinn Emanuel, Spiro has become a bigger and bigger figure in Musk’s orbit over the past few years. He helped Musk win a defamation lawsuit for his comments insulting a cave diver he got into a Twitter fight with over the rescue of a Thai boys soccer team several years ago.

Spiro has also represented a roster of famous athletes and musicians, including Aaron Hernandez in his 2016 murder trial and Jay-Z in a business dispute over a perfume endorsement deal.

The lawyer is now managing the legal, government relations, policy and marketing teams at Twitter. He was also involved in the layoff plan that went into effect in recent days.

David Sacks

Sacks has worked with Musk since the two were part of PayPal’s team in the early 2000s. They both made fortunes when the company sold, and Sacks has invested in a string of successful start-ups since then, including Airbnb, Facebook and Uber. He’s also become a conservative media figure and a major Republican donor who helped fund the successful recall of San Francisco DA Chesa Boudin earlier this year.

In September, he wrote an article advocating for a referendum in Russia-occupied eastern Ukraine asking residents if they wanted to secede from Ukraine and join Russia, an idea Musk later tweeted himself.

Sacks recently appeared in a Twitter company directory with an official Twitter email and the title “staff software engineer”.

Sriram Krishnan

Krishnan helps lead cryptocurrency investments at Silicon Valley venture capital heavyweight Andreessen Horowitz, which invested $400 million in Musk’s Twitter acquisition.

He’s also worked in product development positions at Facebook, Snapchat and, from 2017 till 2019 at Twitter.

On Monday he said he was helping Musk out at Twitter “temporarily.” Krishnan is the only one in Musk’s team that has actually worked at Twitter before.

Other advisors are tech experts outside USA, and helping Elon Musk with ideas, coding, and research.