The Getter Robo Saga is the timeline of the original Getter Robo manga series by Ken Ishikawa and Go Nagai.
The saga goes through the events of the manga and separate from the anime versions. The differences began with the publification of the Getter Robo Go manga which served as a sequel to previous series whereas its anime version was a remake of the original series. It is also notable for building up the characterization of Getter Rays that appeared in later publifications.
Series by Chronology
Getter Robo Hien ~The Earth Suicide~ has been stated to be based on notes from Ishikawa but is not considered to be an official part of the Getter Robo Saga for its ambiguous status.
There is also Getter Robo Anthology, which is a collection of short stories set at some point along the Getter Timeline.