Link

Link is the name of every protagonist in The Legend of Zelda series. There are many incarnations of Link, each possessing the Spirit of the Hero. However, the Link from Super Mario Bros. X: Sea Side Adventure is neither a descendant of those heroes but a descendant of an ancient hero from another world who inherited his Hylian blood. Despite being not possessing the Spirit of the Hero, Link managed to resemble the two Hyrulean heroes whom Wart and others (especially Mario) met before, due to the fact he too is a counterpart of the Hyrulean heroes.

Characteristics
Link doesn't possess the Spirit of the Hero and is a completely different incarnation, despite sometimes being potrayed as the Sea Sidean counterpart of the hero due to his remarkable resemblance. He is the descendant of the Hero of Dreams whom he only inherited his Hylian blood and courage, not Human. Despite that, Link managed to be connected to the heroes of Hyrule, by having the Force Gem of Courage within him. By being connected to them, Link was destinated to become a new hero on his own, which reveals why he looks like them and the Hero of Dreams. And is now able to remember everything the Hyrulean heroes did (he doesn't know how but always remember stuff the Downfall Timeline's Last Hero went through). As Link is now associated with Courage, he rarely shows signs of cowardice and is willing to use his strength and valor to save and help those around him.

Background
One year later after the birth of Sea Side's new lands, Link was born and raised in a dimension called Illusia. He is childhood friends with Zelda. At the current day, the portal that leads to the outside world had opened, both Link and Zelda went outside but were lost. Link was sealed within the Character Block during the invasion of Sea Side by the Koopa Troop and the 8-Bits.

Sea Side Adventure
Link was freed from his Character Block by Mario and friends.

Mario
At first Link met Mario, they began to fight against each other as rivals. But now, they managed to become good friends. As Mario and Princess Peach noticed, this Link is not the same Hyrulean hero whom they met years ago and was confirmed by King Varun to not being a descendant or reincarnation of any of those heroes from Hyrule but a Sea Sidean counterpart of the hero, yet he has an almost identical figure of the Links Mario met long ago. Regardless, Mario still think that he could be a great hero, which encouraged Link to continue moving on and venture with him and his friends.

Princess Peach
Link mistook Princess Peach as Zelda, and intended to take her with him to Illusia. But noticed a difference; her ears. Despite that, they became good companion. Link is the person Princess Peach often teams up with.

Toad
Toad was afraid of Link during the incident between Mario and Link. Toad was still scared, but Link often shows him his good side. Link treats Toad like a younger kid brother (due to his childish appearance), making Toad being fond of him.

Goldian Duck
Goldian Duck had met Link, he had acknowledged that he has a great power within him and noticed his remarkable courage. However, he still doesn't like Link being with Princess Peach because they are often together more than the princess being with Goldian. Noticing that Link is a Hylian, Goldian Duck hates to hear that, thinking that it would make him less of a human and states that Hylians are in fact humans.

Wart
Link had met Wart after knowing that he kidnapped Zelda, and noticed something familiar from the Frog King.

King Varun
King Varun was searching for Link hoping that he would make a good friend of Mario. The king had chosen Link as a new hero of Sea Side and requested him to team up with Mario to save the Forest of Illusion and its dimension, Illusia. Due to his resemblance to the Hyrulean heroes, Varun called him "Hero of Time".

Trivia

 * The developers except Link to have a similar role to that of Ishida Uryu from Bleach.