A human who decides to disclose information that is considered private by some corporation.
Note that refusing to private corporations the right to privacy does not mean privacy is forbidden. It just means that we don’t protect their privacy. Private corporations usually do have private knowledge which they don’t want to share for various reasons (including the fact that they regard it as their business secret or as a strategic decision). And they may expect from their employees and business partners to respect their privacy, and they may legally write this as a condition in their contracts.
When one of their employees or partners shares some data they wanted to remain secret, and when they discover it, they may terminate the relationship and even sue the employee for contract breach. But they cannot sue him or her for whistleblowing.
Whistleblowing becomes an act of public interest, done by an individual who decides to disclose a secret. The whistleblower is ready to suffer by being dismissed and getting accused of infidelity because he or she believes that this is their duty towards humanity.
Note that having no right to privacy does not mean duty to publish your secrets. Perfect transparency is not possible.
Private corporations may have secrets, and they may protect them, but they must do this themselves and at their own cost. They must not get free support of a public legal system.