Right, so one of my [normal, living] Sims got an Opportunity to take the remains of a loved one to the science lab so they could be brought back to life. I didn't have any dead loved ones, so I had my other Sim, a kleptomaniac, go steal something from the graveyard. What she stole was Vernon Carpenter's remains. So my first Sim took them to the science lab, but the experiment didn't go fully as planned, and I ended up with Vernon Carpenter as a ghost, but part of my family. He's completely controllable and is just another family member. I designed for him this snazzy bedroom shown here.