- “I hunt demons. Yeah, you wouldn't know it to look at me. Let's just say there was me, there was a really mean demon, there was a curse, and the next thing I know I'm not me anymore. I'm sitting on some guy's knee, with his hand up my shirt.”
Sid was a demon hunter who was imprisoned in the body of a ventriloquist's dummy.
Human Life 
Much of Sid's early history is unknown. What is known is that he was alive during the 1930s, during which he had a relationship with a Korean Slayer. At some point, he was attacked by the Brotherhood of Seven, a group of demons who were able to assume human form for seven years at a time by harvesting human brains and hearts. The Brotherhood cursed him, imprisoning his spirit in a simple ventriloquist's dummy. The only way for Sid to break the curse was to destroy all seven members of the Brotherhood.
By the spring of 1997, Sid had succeeded in killing all but one of the Brotherhood. The remaining member's human body was deteriorating, and thus it had infiltrated Sunnydale High to find the heart and brain it needed. Sid recruited a Sunnydale High student named Morgan Shay to help him track down the demon, and was enrolled along with Morgan in a ventriloquist's act in the upcoming talent show.
At that time, Emily Djiemanowicz, a dancer in the talent show, was attacked and had her heart removed. Upon learning of this, the Scooby Gang immediately set out investigating. After some research, Buffy Summers, the current Slayer, came to believe that Sid was the murderer, and that he was harvesting organs to become a living human. Sid, however, came to believe that Buffy herself was the final Brotherhood member after secretly watching Buffy punch through Morgan's locker door while searching for evidence. The confusion was cleared up after a subsequent confrontation between the two, and Sid teamed up with the Scoobies to track down the real culprit. Sid proceeded to reveal to Buffy that, since his original body decomposed long ago, he would in fact die when the curse was broken; however, he assured Buffy that he had already lived far longer than most other demon hunters and thus was fine with dying.
Shortly afterward, Morgan was found dead with his brain removed. However, it was subsequently discovered that Morgan suffered from brain cancer, thus making his brain unsuitable for the demon to use. The demon was quickly revealed to be Marc, who was performing a magic act in the talent show, and he had found a suitable brain in Rupert Giles.
The Scoobies and Sid quickly realized this, and got there in time to save Giles. Through teamwork between Buffy and Sid, Marc was defeated and decapitated by Xander Harris with his own guillotine. However, the curse wasn't broken as the only way to kill the demon was to destroy its heart. Though Buffy offered to finish the job, Sid chose to do it himself and with a final "thanks", stabbed Marc in the heart, killing him and breaking the curse. Sid died moments later leaving his puppet form inert.
Sid the Dummy is initially portrayed as the stereotypical "horny dummy" act when the Scoobies believe him to be a simple dummy, only for Buffy to find out later that it is not an act. While relating his history to the stunned Scoobies (shocked at watching a dummy talk), he describes a sexual history he had in the 1930s with a Korean Slayer, even going so far as drifting out of the conversation and into the memory, later snapping out of it and saying "I'm back." He also unsuccessfully attempts to seduce Buffy, and repeatedly flirts with both Buffy and Willow.
Despite knowing that breaking his curse would cause him to die, Sid was accepting and possibly looking forward to it, saying he'd lived longer than most demon hunters. He displayed a greater knowledge of demons than Buffy at the time of their encounter due to his greater experience, knowing that decapitation wasn't enough to kill Marc. When Buffy offered to finish the job for him, Sid chose to do it himself, ending his quest and effectively ending his own life.
Sid returns as a playable character in the non-canon video game Buffy the Vampire Slayer: Chaos Bleeds. He first appears in the opening of the Cemetery level, and tells her where the apparently resurrected Kakistos had gone. He appears again soon after Buffy, Willow, Xander, Faith, and Spike are transported to The First's home dimension. He explains that he had met the First years ago and, as quoted, "royally pissed him off". After his curse was broken in "The Puppet Show", the First stole his soul and placed it in a duplicate dummy body of the one he was trapped in. He tells the Scooby Gang the legend of Cassandra Rayne (Ethan's ancestor, a warrior for The Powers That Be) and Hope's Dagger, the only weapon capable of harming the First. He aids them in retrieving Cassandra's eyes from Sunnydale Hospital, and stays with Ethan Rayne, unwillingly dragged along for the ride by Buffy, while the Scoobies fought the First's minions and retrieved Cassandra's body parts. After the First was defeated, he disappeared in a flash of light, free at last.
Behind the Scenes
- SID is also an acronym for Small Impact Dummy, a family of test dummies designed to measure rib, spine, and internal organ effects in side collisions.