Comcast

Ralph Roberts bought a small cable system in Tupelo, Mississippi, in 1963 and spent four decades turning it into the largest cable operator in the United States. The Comcast name dates to 1969, and growth came through acquisition — the 2002 purchase of AT&T Broadband made it market leader overnight.

Today its broadband and cable TV are sold under the Xfinity brand over a DOCSIS network, and the group also owns NBCUniversal (2011) and Sky (2018). Famously dismal customer-service ratings have never dented the growth — where local monopolies are the rule, the customer's alternatives don't count for much.