|Played by||Richard Jaeckel|
|Debut||Episode 717: Sylvia (Part 1)|
Irv Hartwig was the local blacksmith of the town of Walnut Grove. Irv appeared to be a friendly, kind-hearted man but was actually a stalker and sexual predator who became obsessed with the attractive 15-year-old girl Sylvia Webb.
Irv took to secretly observing her from concealed places. Then one day, when Sylvia was picking flowers in a meadow while walking home from school, Irv ambushed and raped her, wearing a clown mask and knit cap to conceal his identity. Sylvia had become pregnant from the assault.
While Sylvia received no support from her father Hector Webb, who plainly admitted that he blamed her for the assault, Sylvia became very close with Albert Ingalls. As it happens, Albert worked for Irv Hartwig, obviously unaware of his employer's predatory nature. After Sylvia flees her father's cruelty and runs away from home, Albert finds her, and the two plan to elope and care for Sylvia's baby. Desperate for money, Albert begs Irv for a loan, disclosing his plans and Sylvia's whereabouts in the process.
Having learned where Sylvia is hiding, Irv finds her and attempts to rape her a second time, wearing the same disguise he wore during the initial attack. But Sylvia fights back and swings a piece of lumber at her attacker, knocking off his mask and cap, revealing Irv Hartwig as her attacker. Seeking to escape him, she falls off a ladder, suffering critical injury and miscarriage in the process. Irv is then shot and presumably killed by Sylvia's father.
John Carter later became the new Blacksmith.