Who is who in Black Widow?

Black Widow takes place between Captain America - Civil War and Avengers - Infinity War, as Natasha's chosen family is falling apart and she is left alone. This was an excellent starting point for the makers to begin the plot of Black Widow, in which we get to know Natasha more intimately and deeply, and confront her past full of secrets. This past also includes a number of characters who are new to us, the viewers, and we will introduce some of them, as well as some interesting facts about the title character...