Same here. I had never heard of them. Turns out they're a YC'15 startup (https://www.apollo.io/company/). There are no passwords in the data they lost according to HIBP. They seem to collect personal data from various sources and help other companies increase sales.

So not only do we have to worry about websites we actually use being compromised, but we also have to worry about these sketchy third-party companies that have purchased our data being hacked.