Andi Prendergast is the co-worker and the ex-girlfriend of Sam Oliver. She lives at home with her mother, attends college part-time, and is an accomplished prankster - with Ted as her frequent target. Andi is also the only other main character who has seen the Devil at least twice, although she did not know it. Once when he went with a shopping cart to the Work Bench ("Pilot") and once when he placed her in danger in order to motivate Sam to capture an escaped soul posing as a magician ("Magic").
According to Sam, they have known each other for five years. Since Sam started working at The Bench when he was 16, he must have met Andi in the same year. (OR: Sock and Ben mention at some point that Sam has had a crush on her for seven years, meaning they've known each other since they were fourteen.) Andi seemed to have a crush on Sam, or at least harbored some affection, as seen by her numerous attempts at trying to get the two alone together, from Flaming Lips concerts to coralling carts together. Unfortunately, most of these efforts were foiled by Sam's mysterious second occupation as Hell's Bounty Hunter, which Andi knew nothing about. In the meantime, she began dating fellow college student and all-around tool, Greg.
Once Andi broke up with Greg, Sam tried to ask her to be his girlfriend by giving her an expensive necklace for her birthday. Due to the death of her father a few years earlier, Andi said her main desire was stability and she turned Sam down, fearing she might lose him as a friend if things didn't work out.
That all changed when she saw Sam dating Cady. After a near-fatal car crash, she realized that time was short and she wanted to be with Sam. Sam broke up with Cady, and the two have been dating ever since.
Andi finally discovered Sam's secret life accidentally when she saw him and Sock unleash the scythe vessel for the first time. She had followed them and watched Sam behead the incredibly virile, narcissistic escaped soul (Jack King). Initially, Andi declared Sam insane and threatened to go to the police. Sam, Sock, and Ben tried to convince her about Sam's job as the Devil's Bounty Hunter, but Andi refused to believe until she saw Tony change into his true demon form. She ran away, and later told Sam she was afraid of him. It only took her until the end of the episode to figure out that she should have been afraid FOR him, not of him. Andi made a deal with The Devil so he would play another round of quarters with Sam. But Sam lost due to a broken hand. So now The Devil owns her soul too.