Vendor lineage
OpenDNS - the resolver that became a security product
A public DNS resolver acquired by Cisco and rebuilt as Umbrella.
OpenDNS ran a public recursive resolver and was acquired by Cisco, becoming the basis of Cisco Umbrella. Its significance is the move it demonstrated: a resolver that answers queries is also a device that sees every name a network asks for, before any connection is made.
That position is why DNS became a security control rather than only a lookup service. A resolver can refuse to answer for a domain, and refusing is cheap, early and protocol-agnostic - it stops a connection that has not been attempted yet, regardless of which port or protocol the client intended to use.
It is also why a resolver is a surveillance point, and the trade is stated plainly rather than hidden: whoever answers your DNS queries knows every service your network uses, including the ones nobody documented.