People at Acquia or in the Drupal community might snicker at such a question, but if the folks at Gartner and Forrester couldn't easily understand this relationship (and they specialize in researching technology companies like Acquia and software products like Drupal) then I suspect it is not as clear as one might think.
To directly answer this question - Dries Buytaert is the connection. Dries initially released the Drupal CMS in 2001 and Dries co-founded Acquia in 2007 and is the acting CTO.
Dries founded Acquia which is an enterprise software as a service company that provides the following services for companies using and/or evaluating the Drupal platform to power their website:
- Consulting, guidance, demos and training
- Technical services (website hosting, website architecture workshops...etc.)
- Support (backups, CMS upgrades...etc.)
Originally Acquia's focused revolved around growing Drupal, but it seems like that might be changing a bit because Acquia is rolling out a suite of new software products (Acquia Cloud, Cloud Site Factory, Lift and Content Hub) to help clients host, deploy multiple websites, structure their content, and personalize their website content to different users on any CMS. This definitely sounds like they are trying to broaden their market with a slightly different approach than when they first started since they'll be allowing clients to layer these new products/services on top of any CMS (Drupal, Wordpress...etc.).
Essentially Drupal is a Content Management System and Acquia is developing a suite of software to be used by anyone with a website to help them structure their data so that they can scale on any platform.
Please share any insights or questions you have about Drupal and Acquia's connection. I'd love to hear from you.