Colin L. Powell, who in four decades of public life served as the nation’s top soldier, died on Monday. He was 84. In a statement from the family, he died from complications of Covid-19. He had been fully vaccinated and was treated at Walter Reed National Military Medical Center, in Bethesda, Md., where he died, his family said. Mr. Powell had undergone treatment for multiple myeloma, which compromised his immune system, a spokeswoman said.