Spencer Smythe was an inventor that created giant robots called Spider Slayers. He is also the father of Alistair Smythe.
Several years earlier Spencer worked at a laboratory where there was an explosion. Spencer Smythe was unharmed. However, his son, Alistair Smythe was crippled and confined to a wheel chair.
Several years later Spencer Smythe began to work for OsCorp. He was a robotics expert and he made a deal with Norman Osborn to get a hover chair for Alistair if his spider slayer, the Black Widow, captured Spider-Man.
Spencer believed that Spider-Man was a criminal and that sending the Black Widow after him was for the greater good. However, Spencer was unaware that Norman was really working for the Kingpin. After the Black Widow captured Flash Thompson (who was dressed as Spider-Man) Kingpin's guards invaded OsCorp to take Spider-Man hostage. It was then that Spencer learned that Norman was working with the Kingpin of crime and learned that Norman did not want to hand Spider-Man over to the authorities as he originally believed.
The real Spider-Man then arrived and Kingpin's guards ordered Spencer to activate the Black Widow. Spencer at first refused. However, Norman convinced Smythe to activate the Black Widow because if he didn't they would be killed. During their fight Spider-Man knocked the Black Widow into a vat of acid and destroyed it. That caused the chemicals to explode and Alistair believed that his father died in the explosion.
After Alistair Smythe was turned into a Spider Slayer he attacked Norman Osborn whom he blamed for his father's death. However, Kingpin's men arrived and took Norman and Alistair to Crime Central. Alistair was taken to a laboratory and Norman began to talk to Kingpin. Norman said that Smythe should be going after Kingpin because it was his men that caused the explosion at OsCorp which kill Spencer Smythe. However, Kingpin revealed that Spencer Smythe somehow managed to survive the OsCorp explosion. Kingpin found him among the wreckage. Spencer was willing to work for Kingpin. However, Kingpin believed that Spencer's genius should not be wasted. Because of this Kingpin had Spencer Smythe put in cryogenic suspension inside Crime Central. Spider-Man overheard all of this while spying on Kingpin.
When Kingpin learned that Spider-Man was there he had Alistair attack him. However, Spider-Man revealed to Alistair that Spencer was still alive and was being kept in cryogenic suspension inside Crime Central. Alistair then turned against Kingpin.
Alistair managed to escape Crime Central with Spencer, still in cryostasis, and swore that he would one day find a way to revive him.
In the comics
Spencer Smythe was an innocent inventor that read the articles in the Daily Bugle. Spencer believed that Spider-Man was a criminal and build his first Spider Slayer and brought it to the Daily Bugle where J. Jonah Jameson controled it himself to try and capture Spider-Man. Spider-Man was able to defeat the Spider Slayer and Smythe promised to improve his design.
Over the years, Spencer would build more Spider Slayers, but would fail time and time again to capture or kill Spider-Man.
Some years later, Spencer learned that the radiation he used to power the Spider Slayers was killing him and he abducted J. Jonah Jameson whom he held responsible for his current condition. Spencer then handcuffed Jameson and Spider-Man (whom he also blamed for his radiation poisoning) to a bomb. Spider-Man was able to free them and Spencer died believing that he had killed Jameson and Spider-Man.
In the Spider-Man cartoon from 1967 he was renamed Henry Smythe.