King Zora (Ocarina of Time)

King Zora is the leader of the Zora race, father of Princess Ruto, Prince Ralis, and husband of Queen Rutela.

Ocarina of Time
In Ocarina of Time, he sits on his throne at the helm of Zora's Domain, guarding passage to the great Lord Jabu-Jabu, the patron deity of the Zoras. Only when Child Link presents him with a letter from his incarcerated daughter, held from within Lord Jabu Jabu, does he grant Link passage to Lord Jabu Jabu's lair. When Adult Link ventures to Zora's Domain, he finds King Zora and the rest of the region frozen solid: a curse placed on the region that stems from Morpha's control of the the Water Temple, the source of their water. Freeing King Zora from the ice after completing the Ice Cavern will grant Link a Zora Tunic as a gift. If Link already has a Zora tunic, he will offer him a kiss.

Incidentally, it appears that, according to in-game dialog, King Zora and Biggoron are good friends and have known each other for a long time. During the ending sequence of Ocarina of Time, King Zora is shown to be one of the few characters not celebrating the victory over Ganon, instead sitting next to a grieving Mido.

Majora's Mask
In the Majora's Mask manga, it is suggested that Toto may be his Terminan counterpart.

Oracle of Ages
King Zora also appears in Oracle of Ages in death at the "present time", due to an overwhelming amount of sea pollution. To save him, Link must travel to the past and give him a life potion. After this, he will grant Link permission to enter Jabu-Jabu if the young hero cleanses the seas, handing over the Library Key as well.

Twilight Princess
The King Zora in Twilight Princess is long dead. He was Queen Rutela's husband and the creator of the Zora Armor. It is implied by Eiji Aonuma that this is the same King Zora as in Ocarina of Time.

Trivia

 * Wearing the Goron Mask while speaking to King Zora reveals that Biggoron and King Zora are best friends, and have known each other since childhood.