He fought for the recognition of Afrikaans. Preller helped the Afrikaner to awake to the importance of the history of South Africa. He made great contributions to the writing of South African history, through his research and the literature.
He also contributed greatly to making South Africans aware of the legacy of the Voortrekkers and also played an early part in planning the Voortrekker Monument.
Gustav was the son of Commandant Robert Logie Preller and Stefina Schoeman (daughter of the Voortrekker General Stephanus Schoeman).
Later he worked in Pretoria as a shop-assistant, an articled clerk and a civil servant, studying diligently when he found the time. The South African Academy of Science and Art (Afrikaans: Die Suid-Afrikaanse Akademie vir Wetenskap en Kuns) gives out annually the Gustav Preller Award that has been awarded since 1909.