Dragan runs Milton Security and is Salander's boss. He's protective of her, yet can't protect her. They like each other, but he doesn't quite understand Salander. He's attracted to her, but thinks it's because she so different from the other women in his world. She's "a foreign creature" (2.45) like "a painting of a nymph or a Greek amphora" (2.45). He promises Salander he'll never act on his feelings. He is married, after all. But, when he sees Salander chumming it up with Blomkvist, he goes momentarily (internally) mad with jealousy.
Of all the people in the novel, he knows the most about Salander. He even knows one of her deepest secrets, one which makes him doubly nervous about her. What is this secret? Sorry, but it isn't revealed until The Girl Who Played With Fire. You can learn more about Armansky in that book too.