But there are irregular verbs! The big two you need to know are ‘to go’ - ‘ir’ and ‘to be’ - ‘ser’. Luckily, they’re both the same in the preterite. They become: ‘fui ...
There is one verb that is irregular and weak in the past tense, but strong in the the non-progressive participle: do, did, done. A few verbs are strong in the past tense, but weak regular in the ...