> Gwynne Shotwell

From what I understand: As COO (Chief Operating Officer), she's basically in charge of running the company itself and making sure it's running at peak performance. Who to hire, tracking internal goals, evaluating the performance of middle management, etc. Whenever a company has plenty of people not doing anything, has big work bottlenecks, has useless managers, is ignoring laws & oversight, or is otherwise running in an inefficient manner, it is the COO's role to make sure those things get fixed. An engineer may or may not be good at that job. Management-oriented engineers, like industrial engineers, logistics or systems engineers would probably do well at a COO job, as long as they have plenty of managerial experience. A mechanical or electronic engineer that are top of their field but aren't necessarily managers would probably not be able to keep up in that role.

A CEO (Chief Executive Officer) is tasked with executive tasks, and is the primary ambassador for the company. By executive, I mean they are in charge of "making sure things are happening (being executed)". They ultimately decide and shape the directions the company will take in the medium and long term (acquisitions, looming market threats, new product lines, etc), and are also in charge of making sure stockholders and other stakeholders are kept happy. Often enough, they will be the ones who will ultimately face potential big investors, and represent their company in public (interviews and interrogations). CEOs are paid so disproportionately much not because their job is necessarily super hard (it depends, some are way more hands-on than others), but because their decisions carry the largest impact on the company's performance in the long run, so the pressure they are under is massive. A COO hiring a bad project lead, or a CTO (Chief Technology Officer) choosing a cloud service provider that was ultimately terrible, will not be as catastrophic to the company medium-term as a CEO deciding to branch out into a market the company is woefully unequipped to handle, or the CEO failing to secure crucial investments to finish a large project.

So Elon is CEO of SpaceX, Tesla and now Twitter, and he's famously a very involved CEO, at least in one of them at a time (he kind of neglects SpaceX and Tesla while he focuses on Twitter). Very likely, he made the final call on approving SpaceX's Starlink, which deviated from their core rocket-building business. He was also likely the one who ultimately decided Tesla should focus on expanding their production with Gigafactories, and launching Powerwall to branch into infrastructure projects. Not only that, but in these cases, he was certainly very involved in steering the course these projects would take, based upon the recommendations of his subordinates. You'll also recognize that it will be hard for you to name a single current Tesla, SpaceX or Twitter employee aside from him, and that is by design (especially since his companies have the habit of firing their PR teams). As CEO, he focuses all negative attention the company attracts on himself, and ideally liberates his team from that negative attention.