WILMINGTON, Del.—Elon Musk insisted in court that Tesla Inc’s board controls the company but also said the electric vehicle maker would “die” if he wasn’t the chief executive, as he ended his first day of testimony on Monday in defense of Tesla’s 2016 acquisition of SolarCity. The lawsuit by union pension funds and asset managers alleges the celebrity CEO strong-armed Tesla’s board of directors into depleting the company’s assets with the $2.6 billion all-stock deal for SolarCity. The CEO at the time owned a roughly 22 percent stake in both Tesla and SolarCity, which was founded by his cousins, and some Tesla shareholders alleged the deal was aimed at bailing out Musk’s investment in the solar panel company. Kicking off a two-week trial in Wilmington, Delaware, Musk, wearing a dark suit, white shirt and a slightly askew dark tie, testified that he has tried “very hard not to be the …