The verb كَان (was) and its inflections يَكُونُ (to be), كُنْ (be) all represent the meaning of being (existence). They give the nominative case to the subject and the accusative to the predicate.
كَان أَبي حَكِيمًا
My father was wise
وَكَانَ اللهُ غَفُورًا رَحِيمًا
And Allah is ever Forgiving and Merciful. [Quran:4:96]
Its sisters are similar verbs and their inflections which also denote states of existence (being, inception, continuity and duration). They follow the same case rules as Kāna.
ليسَ (to not be)
لَيسَ البَيتُ وَاسِعًا
The house is not wide
أَصبَحَ (to become | associated with morning)
أَصبَحَ الجوُّ ممطرًا
It has become a problem
صَارَ (to become)
صار الوَلدُ طَبِيبًا مَشهُورًا
The boy became a famous doctor
صِرتُ مُهَندِسًا
Became an engineer
أَمسى (to become | associated with evening)
كيف أمسيتَ؟
How are you this evening?
ظَلَّ (to remain / stay)
ظَلّ الوَلَدُ قَائمَا
The boy remained standing
Verbs of continuity:
مازال ، ما برح ، ما انفك ، ما فتئ
مَا زِلتَ شَابًا
You are still young
ما زالَ المَطَرُ نازِلًا
The rain is still descending
مَا فَتِئَ يتذَكَّر
He still remembers
ما دام (‘duration | ‘as long as)
اِعمَلْ مَا دُمتَ صِحِيًا
Work as long as you are healthy