Don Sahlin (pronounced "Sa-lean") (June 19, 1928 - February 19, 1978) was Jim Henson's main designer and puppet builder in the 1960s and '70s, and a key influence on the overall aesthetic of the Muppets.
Don Sahlin's work in puppetry spanned the worlds of television, film, stage, and even stop-motion animation. Born in Stratford, Connecticut, his interest in puppetry led to a brief tutelage under Rufus Rose, puppeteer and builder for The Howdy Doody Show. Drafted into the army but released in 1953, Sahlin put his puppet experience to work on Michael Myerberg's stop-motion animated version of the operetta Hansel and Gretel. This led to other assignments in Hollywood as a stop-motion or effects animator, notably working with the company Project FX on several of George Pal's films. (Pal was the creator of the Puppetoons, whose influence can be seen in many similar Sesame Street vignettes, like "King of 8"). Sahlin's work with Pal included scenes for Tom Thumb (animating various playroom toys) and The Time Machine, for which Sahlin provided effects shots and even appeared on-camera, as the clothing store's window dresser in a pixillation sequence. 
By 1960, Sahlin had moved to New York and was working with puppeteer Burr Tillstrom of Kukla, Fran and Ollie fame, building and re-building Kukla, Colonel Crackie, and Tillstrom's other characters for a Broadway show. It was around this time that Sahlin first met Jim Henson, at a Detroit puppetry convention.
In 1962, Henson contacted Sahlin to build a dog character he had sketched for use in commercials, Rowlf. Don Sahlin soon became Henson's primary designer and builder, beginning with commercials and early projects such as Tales of the Tinkerdee.  He also provided special effects for Time Piece, and assisted on stop-motion projects, such as the animated ham used in the second Wilson's Meats Meeting Film (in which Sahlin has a cameo). In The Muppets on Puppets, Henson introduced Sahlin to the viewers as "doing some of our backstage effects and working some of the puppets" in the 1968 special. In a story-telling skit, he alternated between puppeteering Rowlf's right hand and operating effects like an "explosion". Don Sahlin went on to create and build Muppets for Sesame Street, The Muppet Show, Emmet Otter's Jug-Band Christmas, The Muppet Movie, amongst many others.
Don Sahlin also helped Jim Henson with two of his stop-motion Sesame Street films, "The King of 8" and "The Queen of Six". In a Closeup Magazine interview from 1976, Don Sahlin said "Jim Henson supervised the filming, but he gave me all the freedom in the world to do what I wanted."
Sahlin is the designer credited among Henson staff as the creator of Ernie and Bert, Grover, Cookie Monster and other classic Sesame Street characters. He is "the inventor" of the Muppet look, from a design point of view. As discussed in the book Jim Henson's Designs and Doodles, many of the Muppets began as Henson's rough sketches, which Sahlin then built and modified as needed. This often included special mechanisms or effects; for the La Choy Dragon commercials, this meant "devising a system for this early full-body character to actually breathe fire." Sahlin was known to refer to himself as the "guardian of the essence" of the Muppets.
Beyond building specific characters, Sahlin contributed two significant concepts to the Muppet aesthetic, "the Magic Triangle" and "the Henson stitch." The former was a simple but effective approach to postioning eyes, creating a triangle in relation to the nose and mouth. Jim Henson explained the importance of eye placement: "It would be the last thing [Sahlin] would do, and he always wanted me there, to make sure it was right for both of us -- making sure the eyes had a point of focus, because without that you had no character." 
The stitch is a specific method of sewing cloth as tightly as possible so the seams would be "nearly invisible," thus aiding the illusion of stylized "reality" when characters were filmed in close-up. This technique, dubbed the "Henson stitch" by Sahlin, does not in fact create a truly invisible seam, but worked sufficiently for television purposes (hiding, for example, the seam down the middle of Kermit the Frog's snout). 
Experiments and Explosions
In addition to building assorted monsters and other bizarre characters, Sahlin had his own eccentricities and unique sense of humor, which often resembled the antics of the Muppet characters themselves. Indeed, the character of Crazy Harry was originally named Crazy Donald, after Sahlin's tendency to rig explosions and other intricate devices in people's desks.At MuppetFest, Dave Goelz recalled this side of Sahlin:
Another trick, recalled by Goelz, involved crafting a spring-loaded mouse from gray fabric and yarn wrapped around a bolt, and wound with a reel of rubber band around furniture legs. "He'd just wait until the right moment - wait until everyone was in the right position, and then just pull the ring."
At the same event, Jerry Nelson recalled that Don Sahlin once rigged up a hose over Jerry Juhl's desk. He waited until Juhl was in the office for an hour and a half, then left the room and whispered through the hose: "Jerrrrry... Jerry Juuuuuuuhl..."
Goelz remarked that these jokes may seem weird, but "it's a key part of what The Muppet Show was. Don would never be working on what he was supposed to be working on... That spirit permeated everything that he did, and we caught it. It was all about having fun, and it became very passionate."
Sahlin's creativity was not limited to building puppets or frightening his co-workers. At the New York Muppet Workshop, a group of mice, freed from a hospital, resided in an aquarium in the office. Don Sahlin constructed an elaborate environment for the mice, first using a clear plastic sphere and an assortment of lines and pulleys to create an elevator for the mice. Sahlin later created an aerial highway, "like a mouse freeway", by which the rodents could travel independently across cupboards, to chandeliers, and down to the desks, riding in a Slinky vehicle. 
Sahlin died on February 18, 1978. In his honor, Jim Henson had a bench with an inscription placed in Sahlin's favorite spot on Hampstead Heath, the highest point which overlooked the city of London. (Following his own death in 1990, the same bench was dedicated to Henson himself.) The bench was renewed with new wood and engravings in the summer of 2012.
The final episode of Fraggle Rock was also dedicated to Sahlin's memory. Jocelyn Stevenson recalled that the two tributes were not unrelated. The production team had been stumped in trying to find a name for the small, industrious creatures of Fraggle Rock. Walking on the Heath to clear their minds, Stevenson and Henson stopped to sit on "Don's bench." "And the minute we both touched wood, we said, out loud simultaneously- Doozers! Perfect name! 'I knew Don would figure out a way to work on this show,' said Jim. So we thanked him and went back to work."  Sahlin also continued to receive posthumous credit for his work in creating the Muppet Show and Sesame Street characters, in such productions as The Muppet Movie, Big Bird in China and Follow That Bird.
- Commercials -- built Rowlf, Southern Colonel, Sir Linit, Delbert the La Choy Dragon, Baskerville, Mert, others
- The Jimmy Dean Show -- Maintained Rowlf
- Time Piece -- special effects, cameo as nightclub comic
- The Tales of Tinkerdee -- Built Taminella Grinderfall, King Goshposh
- The Ed Sullivan Show -- Beautiful Day Monster, Sclrap Flyapp, Mahna Mahna, various
- Hey Cinderella! -- Built Splurge, King Goshposh (with Kermit Love), Featherstone
- Sesame Street -- Designer and/or builder of Bert, Ernie, Big Bird (first version of his head, largely redone by Kermit Love), Cookie Monster, Grover, Oscar the Grouch, The Amazing Mumford
- The Great Santa Claus Switch -- Built Thig, Thog, and various Frackles
- The Muppet Musicians of Bremen -- Built Leroy the Donkey, Rover Joe, Rats, and others
- The Frog Prince -- Built King Rupert the Second (with Kermit Love), Taminella Grinderfall
- The Muppet Show -- Built Beaker, Sam the Eagle, Jerry, Lenny the Lizard, Dr. Teeth and "Special Puppets"
- Emmet Otter's Jug-Band Christmas -- Built Alice Otter, Emmet Otter, and others
- The Muppet Movie -- Muppet Designer
- Hansel and Gretel (1954) -- stop-motion animator
- Tom Thumb (1957) -- stop-motion animator (Devils, Other Toys)
- GI Blues (1960) -- puppeteer
- The Time Machine (1960) -- stop-motion animator, actor (as the window dresser)
- The Wonderful World of the Brothers Grimm (1962) -- stop-motion animator (Elves)
- ↑ Pettigrew, Neil. The Stop Motion Filmography McFarland, 2003.
- ↑ *Inches, Alison. Jim Henson's Designs and Doodles. p. 46.
- ↑ Closeup Magazine, No. 2, interview by David Prestone, reprinted here.
- ↑ Inches, Allison. Designs and Doodles. p. 50
- ↑ Finch, Christopher. Of Muppets and Men.
- ↑ Finch, Christoper. Jim Henson: The Works. p. 27
- ↑ Finch, Christopher. Jim Henson: The Works. p.202
- ↑ Durrett, Deanne The Importance of Jim Henson, p. 32