As children during the Ice Age, Crash, Eddie and their mother adopted an young abandoned mammoth called Ellie, making her forget her origins and making her think she's an opossum. In the later years, they are meet by Manny, Diego and Sid who were trying to escape from the flood and soon became part of the gang.
Crash and Eddie spend most of their attempting dangerous stunts such as buggy jumping above lava pits, being catapulted through the air by a tree (with the assistance from Ellie or Manfred) and racing logs.
Although very close lookalikes, it is possible to tell who's who. Crash has a flatter nose and has blue eyes while Eddie has a pointed nose and brown eyes. Eddie also has some hair between his eyes. In some scenes of Ice Age 3 both Crash & Eddie has blue eyes. According to Eddie's comment in Dawn of the Dinosaurs--"Age before Beauty"-- would indicate that Crash is the older brother and Eddie is the younger brother.
Eddie is more of a wimp then Crash and the two love each other very much as shown in Ice Age: The Meltdown, Eddie runs to Crash after Manny shot him out of the tree. They also cling to eachother alot when faced against danger.
It's also possible that Crash and Eddie are references to Lifty and Shifty from the show Happy Tree Friends, or vice versa.
-Crash: You know the best part? We're carrying diseases!
-Eddie: Missed me, missed me! Now ya gotta kiss me!
-Crash: Which end is up?
Eddie: I'd hide that face too!
-Edde: Nice miss!
-Crash: I believe I can fly!!!
-Eddie: Crash, I told you not to drink before bed!
-Crash: I didn't do this! ...At least not all of it.
-Crash and Eddie: Yes Master!
-Eddie: Rudy's tooth!
-Crash and Eddie: Yes Sir!
-Eddie: I can't even look at him!
-Crash: We're very, very stupid!