He was the mastermind behind Home Box Office (HBO), successfully merging his cable service with it to develop Cablevision, a major television and internet provider in the northeastern United States. The Dolan family sold Cablevision to European firm Altice in 2015 for nearly $18 billion. Although beloved for his contributions, Dolan's family's prominence in New York was marked by mixed emotions, particularly regarding the performance of the Knicks and their contentious relationships with broadcasting networks.

At the time of his death, Dolan was valued at $5.4 billion, according to Forbes, leaving a profound impact on the television industry and a notable legacy in American entertainment.