In short, there are two companies calling themselves “Arduino” at the moment. One, Arduino LLC was founded by [Massimo Banzi], [David Cuartielles], [David Mellis], [Tom Igoe] and [Gianluca Martino] in 2009, runs the website arduino.cc, and has been directing and releasing the code that makes it all work. Most of these folks had been working together on what would become the Arduino project since as early as 2005.
The other “Arduino” used to be called Smart Projects and was the manufacturing arm of the project founded and run by [Gianluca Martino]. Smart Projects changed their name to Arduino SRL in November 2014. (A “Società a responsabilità limitata” is one form of Italian limited-liability company.) They have been a major producer of Arduino boards from the very beginning and recently registered the domain arduino.org.
Around the time of the name change [Martino] sold his shares to a Swiss firm Gheo SA and [Federico Musto] was appointed CEO. Gheo SA is owned and directed by [Musto], who also runs a design consultancy based in the US and Taiwan called dog hunter, LLC.