The term was first noted in The Hour of God by Sri Aurobindo and is used by Shasa in Dear Brother. It may refer to:

Artists and Scientists
Authors
Lightworkers (a term I first heard used by Patricia Cori)
Mystics, Prophets and Seers
Yogis and Swamis

Some Examples:
Albert Einstein
Benjamin Franklin
Galileo
Gandhi
George Carlin
Jesus of Nazareth
JRR Tolkien
Mahavatar Babaji
Paulo Coelho
Ramana Maharshi
Robert M Pirsig
Richard Bach
Sri Aurobindo
Sri Yukteswar

and countless, countless other people who have strove so hard for the continuous establishment of the Kingdom of Heaven, a tether to cling on to during the dark ages.