"The leader of this organization was the Minister for Education."
Translation:Pemimpin organisasi ini dahulu adalah Menteri Pendidikan.
Is "dulu" abbreviated from "dahulu"?
Yes, something like that.
'dahulu' is more formal.
'dahulu' is the base word that you use when you're attaching the affixes to form other words.
The Ministry (KemDikBud) has even dedicated a separate page for this:
The first two examples on that page show that 'dahulu' and 'dulu' are interchangeable.
The other examples show that 'dahulu' is the base word for the affixed forms.
That's because the English sentence is not a 100% accurate/identical translation from the Indonesian sentence.
When translating 'dahulu' from the Indonesian sentence, the phrase 'in the past" should actually be included in the English sentence like this :
"Pemimpin organisasi ini 'dahulu' adalah Menteri Pendidikan."
"The leader of this organization was 'in the past' the Minister for Education."