His birth parents, whom he no longer remembered, named him “Kakarot”. Thanks to a bump on his head, he preferred his adopted name. Vegeta addressed him as “Kakarot” anyway, to annoy him.

“Son Goku” became a hateful mantra to his enemies. Arale-chan called him “Go-kun”, a nickname he still sometimes misses. To Bulma, he was “Son-kun”, whereas Piccolo just used “Son”.

Chi-Chi spoke to him as “husband”, even when she was mad at him. He was Gohan’s “Daddy”, but merely Goten’s “Father” in public, and “Old Man” privately.

Pan-chan and Bra-chan dubbed him “Grand-Dada”, because he was always so silly.

Unnecessarily Long and Tiresome Authoress’ Notes:
I had scribbled up an introspective piece, but then I thought Goku wasn’t really much of a person to do any intense naval-gazing and this premise has been done better in other places anyway.