The Wali Songo are the nine saints Javanese tradition credits with bringing Islam to the island. They are associated with the north coast sultanates of the fifteenth and sixteenth centuries, particularly Demak, and each has a tomb that is a pilgrimage site. As a group they function less as a historical roster than as a way of narrating a conversion that took centuries and left little documentation.
Within the group the tradition draws a contrast, and Sunan Kalijaga stands on one side of it. Some of the saints are remembered as strict, insisting that Javanese practice be replaced. He is remembered as the one who worked from inside the culture, who kept the shadow theatre and the gamelan and the older calendar and used them as instruments of preaching, and who is said to have told a ruler that people cannot be pulled to a new thing but can be led to it.
That contrast is doing live work in Indonesia today. Arguments about whether Indonesian Islam has a legitimate local character, conducted under the banner of Islam Nusantara, appeal to him constantly; so, from the other direction, do arguments that Javanese practice needs purifying. A figure with no secure dates and no contemporary record has become a position in a contemporary debate, which is a good reason to be careful about what the stories are evidence of.