He was sent by his pack to retrieve the human baby called Roshan; When he found Roshan in Manny and Sid's care, he pretended to lead them to the humans, but instead planned to lead them into an ambush by the pack.
However, when Manny saved his life, Diego had a change of heart, confessing about the pack and sacrifices himself to help them escape.
Sid's right front tooth was slightly bigger than the left, similar to his right eye, which was also somewhat bigger than the left, both eyes of which were pale green.
Sid's pelt was dirty and tan, and became brown when the fungus it carried dried out, Sid attributing the state of his pelt to his vegetarian diet, which he said led to a younger-looking pelt.
He was seemingly killed by the pack's leader, Soto, but survived and joined Manny and Sid on their travels.
In the second film, he was revealed to suffer from aquaphobia, but he eventually conquered it in order to save Sid, Crash and Eddie.
In the third film, he began to fear that he was losing his predatory abilities from being in the "herd" too long, and considered staying in the underground dinosaur world with Buck.
He changed his mind after managing to save the labored Ellie from a dinosaur attack.
They first made their presence known to the opening characters by means of shooting pebbles through reeds at Sid and Diego, then roasting them so as to humiliate them, but Diego began chasing them, leading both Sid and Diego to Ellie.
When the team escaped they destroy the ship and take Shira with them. Sidney "Sid" is a Megalonyx in all five films who is dull-witted, talkative, friendly, carefree, naive, accident-prone, patient and funny herd member with a caring nature, and is voiced with a lateral lisp.
Little is known from Sid's life other than that Sid once lived in a tree with other sloths that always wanted to leave Sid behind when the migration occurred, using several different ways to leave him behind.
When Manny had saved Ellie from drowning, they helped Ellie back onto solid ground, but almost drowned when the flood was encroaching.
Eventually however, the waters drained, leaving Crash, Eddie, and all of the others alive.