Founded in 1945 in a farmhouse outside Hannover, Sennheiser is still owned by the founding family and brings in roughly a billion euros a year. The pro audio side — broadcast, film sound, live wireless — is what Sennheiser is best known for today.
Sennheiser sells consumer headphones too, but in 2021 they sold the consumer audio division to Sonova (the hearing-aid company). The pro audio business — microphones, wireless systems, conference systems, headphones for broadcast and aviation — is what stays under the Sennheiser name today.
They also own Neumann, the legendary studio microphone maker. So when you buy a Neumann U87, the corporate parent is Sennheiser.