Hi brother,
According to Urantia book ,in my own view and understanding, the PLANETARY PRINCE is the caligastia who was the first Divine revelation of 5th epochal to come and visit our earth, it is estimated to about 500,000 years ago.
PLANETARY PRINCE is known as the prince of Urantia ( earth) of which now belongs to Jesus of Nazareth known as Christ Michael of Nebadon.
For more read Paper 66.the planetary prince of Urantia.
Godspeed.
In reading and understanding the Urantia book brother!!!