As a founder of Cloudera and a participant in the Apache Hadoop community, I'm dismayed whenever the press writes something about Cloudera "creating" Hadoop. No one here believes that, and we try to acknowledge the great work done by the community, especially at Yahoo!, Facebook, Amazon, Powerset, et al., whenever we can.
To the best of my knowledge, we're the only company to provide a commercially supported distribution of Hadoop. I'm pretty sure that's what Ping meant when he says "behind"--supporting, not necessarily solely creating.
Anyways, it's an open source project, and the copyright belongs to the Apache Software Foundation. In the case of Linux, no one organization contributes more than 13% of the code (e.g. http://lwn.net/Articles/222773/). The same distribution of contributions will likely be the case for Hadoop as it matures, and it's reasonably close to that state now: there are subprojects to which neither Yahoo! nor Cloudera is the primary contributor, and it is most certainly not the case that 80% of all Apache Hadoop code comes from any single organization.
Either way, Hadoop is the most interesting open source project with which I've been involved, and I hope the increasing attention doesn't distract the community from its primary goal of producing kick-ass code.
Later, Jeff