Years before Elon Musk set his sights on Twitter, Parag Agrawal, a senior engineering executive at the social media company, was asked in an all-hands meeting what his hobbies were. He nervously replied that he enjoyed growing plants in water, without soil.

Now, as the brazen Tesla and SpaceX CEO moves forward in fits and starts with his acquisition of Twitter, the harsh spotlight focused on Agrawal is forcing him to find new muscle as CEO. His six-month tenure has been an unusual test of his leadership chops.

So far, Agrawal has shown signs of greater decisiveness than might have been expected based on his low-profile MO. He is also quicker to enact change than his predecessor, co-founder Jack Dorsey. In his first week on the job he fired two top executives and established a new leadership structure. In May he ousted two more deputies whom he had just elevated, and promoted Jay Sullivan, product vice president, to general manager of Twitter’s consumer business and interim general manager of revenue. Less publicly, Agrawal established new company wide performance ratings and ways to measure the speed of product launches, with the aim of holding teams accountable, a person familiar with the changes said.