In Golden Sun, there are many important characters that serve to progress the game. Interestingly, through the use of a special code, it's possible to change the names of nearly every major character in the game. Default names shall be listed here.
Isaac is a Venus Adept, one who uses the powers of the Earth and plants. He was born in the town of Vale, and lived there until the age of 17. He is friends with Garet, Jenna, and her brother Felix, until the events at the start of the game. His father, along with both of Jenna's parents and Felix, are lost in a terrible storm that takes place in the game's Prologue. After this, he trains hard to become a powerful user of Alchemy under Kraden, along with Garet. He serves as the main character, party leader, and decision maker for the group. Isaac never speaks during the course of the game, aside from the player's "yes" or "no" responses to questions.
Isaac is a "Heavy" character, capable of wearing the tougher equipment. He can wield Swords, Maces, Axes, and Blades (one handed swords).
Note: This character's name can be changed during the normal course of the game, without the code mentioned above.
Garet is a Mars Adept, with a hotheaded attitude to match his fire-based powers. He was born in Vale, like Isaac, Felix and Jenna. Like Isaac, he is 17, and after the storm that led to the loss of Isaac's father and others, began training with Kraden to master Alchemy. Garet is almost exclusively concerned with their mission, often recommending that they ignore people in need to get on with their mission. When Isaac decides to help them, Garet is embarrassed to admit that he didn't want to. He is also the only character in the game whose entire family seems to be alive and well. His grandfather serves as the mayor of Vale, as well.
Garet is a "Heavy" character, and like Isaac, is capable of wearing tougher equipment and wielding Swords, Maces, Axes, and Blades.
Ivan is a Jupiter Adept, a title which comes with many very different abilities from the others. The thing that sets him apart the most is his ability to read minds, which makes many non-Adepts uneasy. He lived with Master Hammet in Kalay for a long time, but during a trip to Vault, Ivan was responsible for the loss of Hammet's staff, the Shaman's Rod, and was forced to stay in Vault to search for it. Isaac and Garet help him find it, and when Ivan learns that he will be unable to rejoin Hammet for a long time, he agrees to help Isaac on his quest. Ivan is 15, making him the youngest member of the party.
Ivan is a "Light" character, capable of wearing robes and light armor. He can use Staffs and Blades.
Mia is a Mercury Adept, one of only two known members of the Mercury clan, the other being Alex. She and Alex have a history, but it isn't thoroughly revealed during the course of the game. Mia is 17, like Isaac and Garet, and lives in Imil, near the Mercury Lighthouse that she must protect. When Saturos' group storms the Lighthouse, Mia is forced to team up with Isaac and the others to reach the top. After the events at the Lighthouse come to a close, she realizes that she must continue traveling with them to help stop Saturos, Menardi, and Alex. Mia's addition rounds out the party to have one of each element.
Mia is a "Medium" character, capable of wearing the same robes and light armor as a "Light" character but also some of the heavier helmets and other equips. She can use Staffs and Maces.
Saturos is one of the enemies that appears early on. He can be seen as "Mystery Man" in the prologue, hinting that his dealings with Sol Sanctum go back quite a ways. He is the leader of the group that is trying to light the lighthouses. Saturos is a Mars adept, and a member of the Mars Clan, along with Menardi. Apparently, he also rescued Felix from drowning in the river during the storm several years ago. Saturos' singular goal is to light all four of the lighthouses. He is quite calm and collected most of the time, and often shows bravery, despite his willingness to do whatever it takes to get the job done.
Saturos fights with a sword, and isn't afraid to do so alone. He can also use similar Psynergy skills to Garet.
Menardi is a tough woman who has been traveling with Saturos for a long time. She can be seen as "Mystery Woman" in the prologue. She is a Mars adept and a member of the Mars clan. Apparently, she helped to rescue Felix from drowning during the storm many years ago. She, like Garet, is rather hotheaded and impatient, which contrasts with the other members of her group rather sharply. Menardi is also quite devoted in her task to light all four of the lighthouses, and is often the one to suggest their extreme measures.
Menardi fights with a long Scythe, and always does so alongside Saturos. Her Psynergy abilities are essentially identical to Saturos' as well.
Felix is Jenna's 18 year old brother, and a Venus adept like Isaac. He was thought to have been killed in the great storm seen in the Prologue, but Saturos and Menardi saved him. They have somehow convinced him to help them in their quest to light all of the lighthouses. When he is first seen, he is wearing a green mask, but Menardi forces him to take it off. When Isaac and company recognize him, he serves as the enemy's guarantee that they will not harm their hostages, Jenna and Kraden. Felix is never fought as an enemy, and from the point where Jenna and Kraden are captured onward, he serves as their protectors almost exclusively.
Felix's abilities are comparable to those of Isaac.
Alex is a Mercury adept from Imil, just like Mia. He's a mysterious and manipulative character who never fights at all. He is trying to light the lighthouses for his own reasons that are unknown to all of the other characters. He has also gained many new powers, like teleportation, that he did not possess when he knew Mia. He's a member of the Mercury clan, and still has many water abilities.
Other Major Characters
These are characters who are important to the storyline, but don't belong to either party.
Jenna is a Mars adept that grew up with Isaac, Garet, and her brother Felix in the town of Vale. She thought that Felix had died during the storm three years ago, but when Saturos and Menardi raided Sol Sanctum, she learned that he was still alive. When Isaac and Garet go to get the last Elemental Star, the chamber they are in begins to collapse and Saturos' party is forced to take her and Kraden with them. She does join Isaac's party for a short time in the beginning, however.
Jenna is a "Light" character, capable of wearing robes and light armor. Jenna can wield Blades and Staffs.
Kraden is the only main character that isn't an adept. Instead, he is a scholar of Alchemy. Kraden is seen talking to Saturos and Menardi early on, and their visit prompts him to go explore Sol Sanctum with Isaac, Garet, and Jenna. He has a tendency to ramble on with long speeches and monologues, which sometimes bore the other characters (and especially players; Kraden is notoriously disliked for this fact.) Despite this, he is quite knowledgeable, and without his insight reaching the Elemental Stars would not have been possible. Like Ivan, he is originally from Kalay.
The Wise One is a being of great power who lay sleeping in Sol Sanctum. It is because of the Wise One that Isaac and Garet learn of the consequences of lighting the Lighthouses and are sent on their Journey. He doesn't appear often, but he will be important in the events to come.
Spoiler warning! This section of the article contains spoilers, or hints about the game's storyline or progression.
You might want to skip down to the next heading if you do not want facts about the game's storyline or plot revealed to you.
Sheba is a young Jupiter Adept, living near Venus Lighthouse, who gets captured near the end of the game. She gets put with Jenna and Kraden, and is fiercely protected by Felix. During this captivity, she befriends the other captives. When Venus Lighthouse is lit, and earthquakes begin to occur, Sheba falls from the top and Felix immediately leaps off after her. Sheba's past is a mystery to everyone, even her.
Master Hammet is the ruler of Kalay and Ivan's caretaker. When Ivan loses the Shaman's Rod, Hammet is forced to leave him in Vault. Upon leaving the town, they discover that the bridge leading back to Kalay is out, and decide to head north. Hammet is then captured and taken to Lunpa, where the evil ruler of that town, Dodonpa, extorts a ransom from Kalay. Rescuing him is the focus of a major sidequest in the game.
Master Hama is a Jupiter adept from Lama Temple who seems to know Ivan very well. She already knows all about Isaac's party's quest, and has been waiting for them to arrive. She passes on the ability Reveal to Ivan, as well as a young girl from Xian whom she used to test the technique on, Feizhi.
A young girl from the town of Xian, at one end of the Silk Road, Feizhi is the daughter of the Dojo leader, and has a boyfriend named Hsu. Since the eruption of Mount Aleph, she has been gaining the ability to sense future events, and is desperate to reach Lama Temple due to things she has foreseen. She follows Isaac through the Altin Peak mines, and eventually he helps her by rescuing Hsu. They return home to Xian and live happily.
Ouranos is one of two men traveling to Tolbi from Kalay as part of a tour group with his partner, Sean. He is a powerful and brave warrior, and when the ship needs a hand he is eager to provide it. Ouranos, despite his size, has an illogical fear of water. His goal is to go to the Colosso Tournament that is being held in Tolbi and win it. He doesn't make it to the Finals in Colosso, however.
Sean is Ouranos' friend and traveling partner. Like Ouranos, he is set to win the Colosso tournament in Tolbi, and when the ship is in need of warriors to fend off monsters, he reluctantly volunteers. When Isaac returns the Anchor charm to the ship's captain, Sean is the one to suggest that Isaac's party protect the oarsmen during the ride. He doesn't make it to the Finals in the Colosso tournament either.
Babi is the ruler of Tolbi, and a man who is said to have been living for hundreds of years. He is having a lighthouse constructed in his name near Lalivero and the Venus Lighthouse.