Doubleclick were one of the first companies to sell ads online, on a large scale. In the early 2000s, selling ad space became the de-facto way to fund your online business , which fed the bubble that eventually led to the 2001 financial crisis:

Companies were flush with cash from wave after wave of seed investment. So naturally, they had plenty of money to buy ads, usually in other Internet companies. Startups bought ads and published them on the sites of other startups. Doing so inflated everyone’s value.

And of course, Doubleclick also birthed the idea of using cookies to track online behaviour, what ads we see and what ads we click.

By shifting the source of the cookies to a single domain under their control, in this case the DoubleClick servers, data between sites could be aggregated and distributed, as long as each site agreed to install a snippet of code that gave DoubleClick partial access to their data.

So here we are, more than twenty years later, and it’s as if nothing has changed.