Goku has died 5 times, but only twice in the canon timeline. He sacrificed himself to defeat Raditz and shielded the world from Semi-Perfect Cell’s self-destructive blast.
Sacrifice Against Raditz
His first death involved a sacrifice to save Gohan from Raditz. Goku put his brother in a full nelson headlock while Piccolo charged up his Special Beam Cannon, receiving the second layer of the blast as it passed through Raditiz.
Goku knew the Dragon Balls could bring him back, so his death was not as worrisome to the main cast as future situations.
Sacrifice Against Semi-Perfect Cell
Goku’s second death involved his sacrifice during the Cell Games Saga. Gohan’s Super Saiyan 2 transformation overwhelmed Cell, urging him to do a self-destructive blast as a last ditch effort. Goku was dead for 7 years after he used Instant Transmission to bring Cell’s explosion to King Kai’s world. He sacrificed himself, King Kai, Bubbles and Gregory in the explosion.
Does Hit Kill Goku?
You may have heard Goku died a third way in the canon timeline, but its inclusion is nearly a technicality. Hit does kill Goku, using his Phoenix Eye Fist. Goku launched a Ki Blast into the air before being hit, the blast landing on and resuscitating his body.
This takes place during the anime-only arc “Future” Trunks Saga, unpresent in the manga. Goku’s death did not require the Dragon Balls to bring him back.
Zamasu Kills Goku
In an alternate timeline where Zamasu was not destroyed by Beerus, the Supreme Kai Apprentice killed Goku and his family. This timeline is not the main one, so Goku’s death in this situation is not comparable.
Heart Disease Timeline
Lastly, Goku died from a heart virus during Future Trunks timeline. Future Trunks came back 20 years in time to deliver medication to cure Goku while warning him of an imminent threat in Androids 17 and 18.
Goku never dies permanently, although his deaths put pressure on the other Z Fighters to revive him in opportune times to rejoin the battle. Frieza does not actually kill Goku, so not every major opponent he faces poses a mortal threat.
Goku has died 5 times total, but twice in the canon timeline. He sacrificed himself to defeat his brother Raditz and he used Instant Transmission Semi-Perfect Cell’s self-destructive blast.