"Zelda II: The Adventure of Link is an action role-playing game developed and published by Nintendo for the Nintendo Entertainment System, and it is the second installment in The Legend of Zelda video game series. It was originally released in Japan on the Family Computer Disk System less than a year after the release of the original The Legend of Zelda. Nintendo released Zelda II in Japan on January 14, 1987, seven months before the United States saw the release of the first Zelda title. Nintendo released Zelda II in North America in 1988, two years after its initial release in Japan, converting the game from its initial Disk System format to the NES cartridge.
The Adventure of Link is a direct sequel to the original The Legend of Zelda, again involving the protagonist, Link, on a quest to save Princess Zelda, who has fallen under a sleeping spell. The Adventure of Link's emphasis on side-scrolling and RPG-style elements, however, was a significant departure from its predecessor. The game was highly successful at the time and introduced elements that would become commonplace in future Zelda games. It was followed in 1992 by The Legend of Zelda: A Link to the Past for the Super NES."
Source: Wikipedia, "Zelda_II:_The_Adventure_of_Link," available under the CC-BY-SA License.