What is danglars profession? How is this important to the plot?

He is a banker, and this is how he will be ruined.

"The Count also sends a telegram to Debray in this chapter relating a contrived news bulletin of a political chaos in Spain. Debray thus rushes to Danglars' wife telling her to recommend to her husband that he sell all his Spanish bonds. He does so, though he loses money. At the end of the day when the news is proven false, the bonds rise to twice their original value. The net loss for Danglars is thus a million francs."