Used to Be a Sweet Kid/Playing With

Basic Trope: A villainous character was at one point a normal, innocent child.

Straight: Jeff Slaughter, the Big Bad, was once a friendly and ordinary little kid.
Exaggerated: While he was a cheerful and saintly child, Jeff becomes a Complete Monster who destroys planets for kicks as soon as he hits adulthood.
Justified: Even villains were innocent at some point in time. Some t hing had to make them bitter and twisted.
Inverted: Jeff is an Evil Overlord as a baby, but calms down and becomes good when he grows up.
Subverted: The heroes learn that Jeff tortured animals as a child and cheerfully engaged in sociopathic behavior.
Double Subverted: As a baby, however, Jeff was completely innocent. Parental Abandonment turned him to this disturbing behavior as a young boy.
Parodied: As a little kid, Jeff liked to play with butterflies, teddy bears, sing praises of Jesus, heal cancers and stand around being all beamy and smily before becoming an Omnicidal Maniac.
Deconstructed: As a child, Jeff Slaughter was good-natured and was completely harmless. However, all the abuse he put up with slowly drove him to take out his anger on the world. He destroyed his memories of the past and became the Big Bad.
Reconstructed: Jeff Slaughter secretly thinks the best years of his life were when he was younger, and kept a single toy to remind him of his previous goodness.
Zig Zagged: Jeff Slaughter, as a child, liked to draw war machines, not out of malevolence, but because he liked to invent things. His parents took this as an alarming sign, mistook him for a Creepy Child and shunned him. As a result, Jeff became really disturbed.
Averted: Jeff's childhood is never shown.
Enforced: "What was Jeff Slaughter like as a baby? He wasn't evil then, was he?"
Lampshaded: Jeff's Supervillain Lair is filled with photos of himself in happier times, in contrast to the death traps and torture devices he has developed since then.
Invoked: "You don't know what I was like as a child! I was happy then! They made me what I am today!"
Defied: Jeff destroyed all evidence of his childhood when he became evil.
Discussed: "What was Jeff Slaughter like as a kid? He wasn't always a Complete Monster, was he?"
Conversed: "It's creepy to think that Jeff Slaughter was a kid like you and me once." "Yeah, Children Are Innocent, right?"

Too bad about Used to Be a Sweet Kid. He used to be such a sweet trope...