Personal workers
From Toadwater Guide
Personalized Workers are obtained from Donating to the game. They work just like regular workers (although the situation may change in the future). These workers will never quit until the worker time from the donation runs out (currently 30 days). You can have four personalized workers - as well as the normal three regular workers. This means you can have total of seven workers at your command for a given time.
When you donate for personalized workers, you also get a Personal island for the same length of time.
You choose the name for your personalized workers and your island, and when your donation runs out, only you can rehire them by donating again, hence they are your personal workers, no-one else can use them.
Personalized Workers start with base stats, so they will be very slow starting. Since they are your workers for 30 days, there is no need to rush to rehire, or to make sure that they constantly have work to do. However, to increase your Management skill and the workers' skills, you will want to keep them busy as much as possible. You can view your Personalized Workers' skills, as well as the skills of your hired workers.