Sam the Snowman is a character from the Rankin/Bass special Rudolph the Red-Nosed Reindeer. He serves as the special's narrator, telling the story and performing songs with the accompaniment of his banjo, and inviting the audience to "pull up an ice-block and lend an ear."
Sam was the first of many Rankin/Bass narrators, usually caricatures of their celebrity voice actors. In this case, he possesses Burl Ives' trademark beard, girth, and voice. He seems to exist entirely outside of the main plot events, relating an item of past history but never directly interacting with the other characters, although he does mention that he told Hermey and Yukon Cornelius where to find Rudolph when they returned to the North Pole. At the end, he is seen watching Santa's sleigh take off into the sky.