The evolution of Elmo. This article excluded variant puppets (used for certain shots or actions) that are visibly different the ones used on a regular basis.

Image As seen in / Year Notes
Season 11
(1979 - 1985)
The first Elmo puppet, introduced in the 11th season. The puppet is used primarily as a background monster in sketches and songs with no established identity (though often performed by Jerry Nelson). The following season, he receives his name and has a recurring role throughout the season, performed by Brian Muehl.
Season 15
(1984 - 1986)
Elmo is briefly taken over by Richard Hunt until the role is taken over by Kevin Clash, solidifying many aspects of Elmo's character.
The puppet used here is a modified version of the previous, with some slightly shaggier fur.
Season 18
(1986 - 1989)
Elmo receives a modified head, with a less bulbous noses, and his hands are armatured.
Season 21
(1989 - 1991)
The puppet is rebuilt again, with some extra scraggly fuzz dangling off the sides of Elmo's head.
Season 23
(1991 - 1993)
Elmo's fur is matted down considerably.
Season 25
(1993 - 1996)
Elmo remains basically the same, but with altered amount of fur.
Season 28
(1996 - 1997)
Elmo's fur is less shagged than the previous puppet and his head is redone, giving him a different shaped mouth. His nose is also noticeably smaller.
Season 29
(1997 - 1998)
This puppet is slightly bigger and has increased fur, similar to his mid-80s appearance.
Season 30
(1998 - 2002)
Season 34
(2003 - 2008)
Elmo's head appears to be larger and the fur is combed down evenly around his head.
Season 44
(2012 - 2014)
This version is considerably furrier, especially on his upper jaw.
Design sketch
The first sketches of Elmo by Caroly Wilcox (cited in Imagination Illustrated as 1979), reveal that he was initially intended to have a wider face.