Google's Doubleclick history:
Official Google Blog: Three years of Google + DoubleClick by the numbers, and video arrives on the DoubleClick Ad Exchange
In 2008, we acquired DoubleClick, and our efforts to make the display advertising landscape a better, simpler place for users, publishers and marketers began in earnest. Today marks exactly three exciting years together. The time has flown by, and we’ve made huge strides towards our goal, largely powered by DoubleClick’s technological and industry expertise.