Tim Janklow was a hunter familiar with the Winchesters, whom Sam encountered while on hiatus in Garber, OK.
Background
Tim Janklow, with fellow hunters Steve Bose, Reggie Hull, were in Garber to investigate the apocalyptic signs occurring in the area. They visited Sam as he was working at Hoyt's bar, where he was using the name 'Keith'. Tim called out Sam's name within earshot of waitress Lindsey, and she commented on the oddness of "Keith Sam." Tim sort of attempted to maintain Sam's alias by telling her that 'Samuel' was his middle name. She continued to needle about Sam's business by asking the trio if they were friends of his; Steve told her that they were old hunting buddies, along with his dad. She asked if they'd hunted deer and things, to which Tim replied, "Yeah... and things." Sam hurried them away to a table.
Tim told Sam that Bobby had called them and that they'd confirmed that Sam was right in sending up the alert about the apocalyptic omens. They'd found evidence that demons were gathered there, so they wanted to know why Bobby told them that Sam was off limits. Tim pointed out that all hands were needed on deck. Sam would only tell them that he was sorry, but he couldn't help, for personal reasons. Not satisfied with that, Tim pressed, wanting to know what baggage was so heavy that it couldn't be stowed in light of the looming Apocalypse. When Sam began to offer another apology, he was interrupted; they heard him the first time. The three hunters left it at that, half-joking that it only meant more demons for them, and declared that the beers would be on Sam when they returned. Sam wished them good luck.
Later, Tim returned to the bar after closing time, obviously battered, and awkwardly asked Sam if he had something to tell him. Sam replied that he didn't and asked him where Steve and Reggie were. He replied that Steve had his guts ripped out during a run-in with a pack of demons. He demanded that Sam tell him the truth about "some crazy things" a captured demon had uttered about him. Reggie then entered the bar, dragging Lindsey along and holding a huge hunting knife to her throat. After convincing Reggie to put the knife down, Sam finally gave into Tim's demand and admitted that he started the Apocalypse.
To Sam's horror, Tim produced a vial of demon blood and declared that Sam was going to drink it, "hulk out", and use his ability to destroy the demons that murdered his best friend, or Lindsey would die. They forced the blood into Sam's mouth and held their hands over his mouth and nose to force him to swallow. Sam slowly got on his feet and spit the blood back in Tim's face, sending him reeling. He then neutralized Reggie, and eventually got the best of Tim and brought the hunting knife to his throat. He released him only when he looked up and saw horrified Lindsey glaring at him.
Sam shoved him away and told them to go, which they promptly did, with a warning that they'd be back. Sam shouted back that he'd be there.