Goku is a pretty interesting character. He's modeled on Son Goku (same name even) who is a character from classic Chinese literature. In A Journey Into the West, Son Goku is an anthropomorphic Monkey King with impressive physical strength. His old wizardish mentor/controller keeps his savage side in line with a crown that tightens when he thinks/does unacceptable things.

The Son Goku in the OP is the protagonist of Dragon Ball, an 80s-90s Japanese comic book and TV show that started as a jaunty sex/gender farce based on A Journey Into the West, kind of in the way Dino Riders is based on paleontology.

It's by Akira Toriyama, a famous comic book artist whose most major past work had been Dr. Slump, a story about a lonely fat inventor who creates a little girl robot. It had lots of jokes about gender and sexuality, like Dragon Ball after it. Both comics would be too racy for American youngsters, but social standards are different in Japan.

Anyway, Goku looked like a little boy, but had a monkey tail, and grew up in the wild with his hermit adopted grandfather who died when he was very young. Because his adopted grandfather was some sort of kung-fu master, and because he has superhuman strength (by virtue of being a monkey king), Goku is nearly indestructible, but totally naive to things like the differences between men and women. One of the running gags early in the series is he innocently "pat pats" people's crotches to determine whether they are male or female when he meets them.

So, people treat him like the small child he is, but when some crazy bad guy shows up and he kicks the guy's ass without effort, everybody is kind of shocked. He represents a comic take on human energy without the controls placed on it by society.

In the beginning, the comic is about him teaming up with a boy-crazy teenage girl who is seeking magical artifacts (the eponymous "Dragon Balls" that will let her wish for her first boyfriend). They then meet a handsome desert bandit with terrible social anxiety who also wants the artifacts to help with his dating life, and a perverted shapeshifter pig who intends to use them to wish for women's underpants. The characters correspond roughly to character in A Journey Into the West, but it's about insecurity, dating and relationships and has a fun, quirky vibe with some action thrown in.

The quests happen in cycles -- you gather all the Dragon Balls, then a magical dragon appears, the person with the Dragon Balls makes a wish, the dragon grants the wish -- that's the end of the story for now, and then the relics scatter around the world at random, and you have to wait a year before going to look for them again.

It stays jaunty, funny and self-deprecating in a lot of ways for most of the series, but gradually changes into something more serious and action-oriented.

Basically all the people on the journey are doing these battles wishing for love and all this, and then people start actually dying (starting with the dad of one of Goku's random friends).

The introduction of death and mortality makes Goku very upset, and he decides he is going to dedicate his quest for the relics to bringing innocent people who were killed by bad guys back to life.

Along the way he meets his best friend (a child Shaolin monk), and they train kung fu with a dirty old kung fu master who lives on an island and reads porno magazines a lot. There's a plot where you learn of two rival kung-fu schools -- an evil one where people use their powers for external reasons and to gain power, and the one Goku belongs to that believes in training, fighting and self-improvement because it is fun and they like doing it. The implication is that enjoying what you do and doing it with gusto make you a better person, a happier person and a stronger person. This is part of the comic's general arc as a sex farce, which is that people's silly desires are part of what make them awesome, and we shouldn't be too critical of things like sex drives and porno. Which is a pretty awesome moral.

Meanwhile, the bad guys who are also looking for the magical relics to make wishes that usually involve conquering the world in some way, go from being minor comic relief to being much more sinister and threatening.

And then Goku's best friend is killed by a demon.

At this point, the comic and Goku change a lot. Goku is really after the Dragon Balls now, but he also wants to train and become as strong as he can so he can defeat the demon and stop him from killing anybody else. It gets very personal for Goku. His tail has been chopped off at this point (for unrelated reasons), and he starts growing up. (The comic and show ran for a really long time, so we see the lion's share of Goku's life with only a few timeskips.)

At this point, the comic has cast aside almost all its pretense as a sex farce and becomes a Shonen action comic about battling evil. It's still quirky, funny ironic and self-deprecating at times, but it's a lot more serious.

After a year or two of this, there is a HUGE timeskip. This divides the comic (and the TV show that ran alongside the comic) into two halves, which are only really distinguished in the U.S. -

Dragon Ball

and

Dragon Ball Z

(The "Z" doesn't really stand for anything important, as far as I know. The comic and show are kind of like that - lot of weird non-sequiturs that are never fully hashed out. Like, at a couple of points you briefly meet the King of the World, who runs the global government. He's a talking dog. This is never explained.)

Dragon Ball Z continued the serious story about Goku as a world-saving kung-fu master who trains to fight bigger and badder enemies and bring innocent people back from the dead. It was a lot more popular in the U.S. than Dragon Ball was -- so much so that Americans almost always talk about "Dragon Ball Z," as if the earlier, funnier Dragon Ball didn't exist.

Goku as a character maintains his optimism, good spirits, and general motivation of doing what he does because it is fun and he loves to do it, which is cast against darker and more sinister rivals with opposing worldviews. Also, Goku is retconned/revealed to be an alien from a distant planet, and the comic departs from A Journey Into the West and becomes a bit of a sci-fi space opera.

If this sounds too amazing and crazy to be possible, it basically is. It's one of the most amazing/crazy/impossible works of art ever. There's a reason it's one of the best-selling and most popular comic franchises of all time.

Every story arc of Dragon Ball Z, the stakes rise higher, to and past the point of absurdity. Goku is so good at kung fu it is trivial for him and fighters on his level to destroy planets. There are arbitrary measures of "power level" introduced at the beginning of Dragon Ball Z that start in the 5-100 range, and by the time they are abandoned about halfway through the second half of the series, they are well into the millions. At one point the characters realize the only way to push their limits is to be beaten nearly to death and to be revived and healed over and over, and there is a series of times this happens to each character in a sort of race to be the strongest. They do push ups in 100x gravity with weighted clothes on until they collapse. They go to special rooms where time passes faster on the inside than on the outside so they can spend years training in hours.

Goku also gets married and has a kid -- his son Gohan, who grows up over the course of Dragon Ball Z in much the same way Goku grew up over the course of Dragon Ball -- except Gohan's problem is he is too civilized -- he and his mom both want him to be a scholar, and he is insufficiently tough and violent by nature to fulfill his responsibilities at times as the son of one of the most poweful beings in the universe (a difficult job for anybody).

In the last couple seasons of Dragon Ball Z, the comic and show become increasingly meta -- the characters at times become parodies of themselves, they are made to do silly dances, you are introduced to characters who pretend to be part of their "crowd" of super-fighters who actually have no abilities and have to fake it, and there is this big fat gluttonous monster who kind of represents all their arrogance and excess. After about two years of attempts to stop him that all fail due to arrogance, this monster destroys the Earth and threatens to destroy the entire universe.

And at the very end of the comic book / TV show, Goku and his archrival Vegeta (who starts as an enemy and becomes a reluctant ally over the course of the story) use the Dragon Balls to bring everyone on Earth back to life, turn to the audience and ask everybody in the world to raise their hands and give Goku some of their life energy so he can destroy the monster. This is the scene portrayed in the OP.

The idea is again to get away from this idea of externality and self-obsession that has been the "villain" throughout the series, and get to the shared joy of striving and betterment that is presented as "the good" by Toryiama.

It's a really powerful scene and an extremely dramatic way to end a series that ran for well over a decade. And it comes right after a big monologue by Vegeta on who Goku is -- which is somebody who is "a true champion" because he doesn't fight because he has to, and he doesn't fight to defend anything, he fights because he is doing what he loves, and that happens to correspond to the people that he loves and the life he leads of continuous self-improvement.

TL;DR -- Goku is the hero of one of the best stories of the second half of the 20th century.