I agree with the earlier post about how Hojo doesn't fit a lot of the criteria for a sociopath. Sociopaths are described as superficial and charming, and have a glow and calmness about them that draws people to them. Like Kefka, probably.
Hojo is sluggish and depressed looking. He is portrayed as someone low in self esteem. Slouched, grumpy frowning face, long greasy hair sloppily tied back with a rubber band like he doesn't care to bathe or fix himself up, and in Crisis Core he just stands there with this defeated, broken posture and has a sloppy, lazy, and unconfident walk. I have heard Hojo being described as a narcissist as well as a sociopath. Does he socialize a lot? Does he lie, act superficial or charming, have a lot of connections, focus on his appearance, try to be the center of attention, etc.? Not at all. He is socially withdrawn, and if anything looks like someone with low self-esteem. I thought narcissists and sociopaths have lower rates of anxiety and depression, are confident and social, etc. which is not Hojo at all. He's a selfish jerk, sure. But a lot of people are without neccissarily being sociopaths.
He's a horrible scientist. Everyone in the game thinks so. Vincent described him as being a queer fellow and lacking in scientific talent, and Sephiroth described him as being a walking mass of complexes and a second rate scientist. My personal opinion? Hojo is not truly a scientist at heart, but he pretends to be. He was obsessed with proving the existence of a higher power, and even in Crisis Core he claimed to have read Loveless thinking that it could aid his research, but that it was pure drivel. How exactly can an ancient epic, a story, aid scientific research? Unless he secretly does believe in a higher power, or wants to believe, but can't which is why he tries to use science to prove it. Even after Sephiroth's death, he still refers to him as "the hero" which means that he stilled believed in Loveless.
He thinks putting humans in tanks filled with mako energy is science, but it's not. In the official artworks, he is portrayed as looking to the side, particularly the left which is often body language for dishonesty.
All of you are wrong. He and the others assigned to the Jenova project had the goal of creating a being with the powers of the ancients. Perhaps to study, to just see if they could, or because Shinra wanted them to so he could use that being to find the Promised Land and create his Neo Midgar. That's it. No super soldiers, no God being, no superior being of any kind. Then after its discovered that Jenova and Sephiroth are not ancients, they put Sephiroth in soldier because they couldn't do anything else with him.
Hojo did not plan the Nibelheim incident. In Crisis Core it is stated that Tifa reported monsters in the area and so Shinra sent soldiers to investigate. That's it. You guys are over thinking this and making Hojo look more evil and scheming than he really was. However, how he is portrayed in the original game and Crisis Core is not the same Hojo in Dirge of Cerberus. In DoC he is more sociopathic but in the others, calmer and more sluggish and depressed looking.
My final conclusion? Hojo cared about Sephiroth to an extent. He had a fanclub for him (that mentioned his shampoo, when he hung out with Genesis and Angeal, exclusive photos, etc.)
That means that Hojo was paying attention to Sephiroth on a level outside of scientific study. After all, was Hojo interested in Red XIII's or Aerith's bathing habits or hang outs with friends? Hojo probably intended to reveal that he was Sephiroth's father when he arrived in Nibelheim after Sephiroth's death, as stated in Hojo's missions in Crisis Core. Lets also not forget his stunt to give Sephiroth more power, and in BC he stays at Shinra just for Sephiroth. (Chapter 10). He obviously doesn't want attachments for whatever reason. Tough love? Or to study the specimen with emotions getting in the way. As for Lu, well in the original game there wasn't much to go on. He might have loved her and accidentally gotten her knocked up and thought it was a good opportunity to use the child, and he got bitter because he was secretly offended st Lucrecia's affair.