Questions & Answers about Saigrač je obećao da će doneti grickalice.
je is the auxiliary verb used to form the Serbian past tense.
So je obećao = promised.
More literally:
- je = is/has as an auxiliary
- obećao = past participle of obećati (to promise)
Serbian commonly forms the past tense with:
- a form of biti (to be)
- plus a past participle
So:
- On je obećao = He promised
- Ona je obećala = She promised
Because obećao is the form needed for past tense, while obećati is the dictionary form / infinitive.
Compare:
- obećati = to promise
- obećao = promised (masculine singular)
- obećala = promised (feminine singular)
Since the sentence is talking about something the teammate already did — he made the promise — Serbian uses the past form obećao.