Shadow Archetype: To Guinan. Being the same race, both experiencing the Nexus, they essentially share a backstory. Soran is what happens when those mystical powers are used for evil instead.
Straw Nihilist: After his homeworld's destruction, he's haunted by the inevitability of death, to the point that he no longer cares who suffers from his plan to return to the Nexus.
Ungrateful Bastard: The Enterprise crew rescue him after the attack on the Amargosa station, and he repays them by nearly getting them killed. Twice.
Used to Be a Sweet Kid: If what he said to Picard was true, he claims he wouldn't have hurt a fly before his world was destroyed.
Woobie, Destroyer of Worlds: He lost his homeworld and family to the Borg, and then he lost his ideal fantasy in the Nexus when he was beamed aboard the Enterprise-B. He's now willing to destroy entire solar systems as part of The Plan to return to the Nexus.