Sidney, known more commonly as Sid, is a ground sloth who was part of a herd of different animals after a number of adventures and experiences brought them all together. He is the tritagonist of Ice Age and Ice Age: The Meltdown, the main protagonist of Ice Age: Dawn of the Dinosaurs, the tertiary tetartagonist of Ice Age: Continental Drift and the tetartagonist of Ice Age: Collision Course.
Born into a family of sloths that went on to abandon him well into his adulthood, Sid met a mammoth named Manny and a saber-tooth tiger named Diego as the three of them made a journey through a tundra to return a human baby named Roshan to his tribe. Following the journey, the three animals remained the best of friends, forming their own "herd".
Not long after, Sid and the others made a new home in a valley that would soon flood, due to the massive amounts of melting ice and snow. During the trek to leave the valley and reach safety, Sid and the others met a female mammoth named Ellie, along with her adoptive possumbrothers Crash and Eddie, and Manny, through Sid's urgings, found a wife in Ellie, taking her and her brothers along with them as part of their herd.
Sid had attempted to assume responsibility further on, taking a group of young animals on a hike through the woods so that he might take on a stance of leadership. Throughout the entire hike, Sid made mistake after mistake, from disturbing a beehive to licking poison ivy. At the end of it all, however, Sid went on to make his mark in the world when he mistakenly set forth a turn of events that saw the creation of the Grand Canyon.
Further on, Sid, growing lonesome as he saw that Manny and Ellie were expecting but he was not, took it upon himself to "rescue" three giant dinosaur eggs, raising them up as his own children. Their mother returned for them, taking her young and Sid back to their own world, where Sid shared parenting responsibilities with the dinosaur mother for a time before returning home with his own herd, which had just seen the arrival of a new member: Manny and Ellie's newborn daughter, Peaches.
In time, Sid, along with the others in his herd, awaited Christmas and the arrival of Santa Claus, though Sid, attempting to start a new Christmas tradition, mistakenly smashed Manny's Christmas Rock, prompting Sid himself, Peaches and Crash and Eddie to head to the North Pole to convince Santa to take them all off his "Naughty List". The herd joined in and began a number of holiday traditions, from Santa enlisting reindeer to pull his sleigh to taking on mini-sloths to build the massive amounts of presents.
Some years later, Sid remained a part of his herd when his own family returned looking for him so as to push off their wizened old Granny on him, leaving them both behind. Sid, downhearted at this, still took care of his grandmother as they, along with Manny and Diego, grew separated from the herd as the continental drift forced them apart and the four met a group of pirates, which they underwent a number of ordeals with before returning back to the rest of their herd, and a means of finding a new home after they were forced from their own due to the continents shifting.
Years later Sid was beginning to yearn for true love, given that he got dumped by a female sloth named Francine. He along with the rest of the herd were forced to leave their home to stop an asteroid from destroying the planet. During their journey Sid met a beautiful sloth named Brooke who ended up becoming the love of his life. Not only did Sid find true love, but he and the herd ended up diverting the asteroid, saving the planet.
He can be briefly seen entering the Oasis.