The Dollars started out as an internet hoax with the original concept coming from Mikado Ryugamine and two other online acquaintances. The idea was to create a gang with no color and be transparent but no one knew who was a part of it. The three went on to other websites and forums to post about the activities of the Dollars and eventually Mikado created a site for them that was password protected. It was meant to be a small project with a few hundred members until member Izaya Orihara leaked the password and the numbers jumped from the 400s to the thousands.
After that, crimes began occurring around Ikebukuro with people pointing to the Dollars as the culprits, some going so far to admit anonymously that they did it and were a part of the Dollars. The other two founders left soon after as Mikado tried to figure out what to do. He posted that the Dollars should be a group of good guys to balance out the bad reputation. Initially rebuffed, he sees on the news how some people cleaned up a bunch of graffiti overnight by the derelict Dollars, something he suggested the other night. As soon as Mikado asked that the Dollars become a good image in the world, the actions of the group changed dramatically.
When Mikado moves to Ikebukuro and organizes a mass meeting of the Dollars to combat against Namie Yagiri and defend Mika Harima, it is shown that a large population of Ikebukuro are members of the Dollars including Izaya Orihara, Shizuo Heiwajima, and even the Headless Rider Celty Sturlson. They all communicate via text messages and emails with online aliases without knowing who one another is unless they are friends.
However, it is because of the Dollars movements and actions that causes the Yellow Scarves to emerge once more first under its old leader Masaomi Kida and then getting taken over my Horada, a member of the gang the Blue Squares. Masaomi becomes especially involved after the incident with the Slasher as he vows to avenge Anri Sonohara who was attacked when in truth she became the Slasher after the incident. Reports began to fly in about random people getting jumped by the Scarves since no one knows who the Dollars are and their leader. Mikado tries to disband the group thinking that everyone will be safe but he brings the group back together once they help fight the Yellow Scarves, realizing that the Dollars are an important part of Ikebukuro.
To this day, only a handful of people know Mikado created and leads the Dollars.