Is Game Boy Advance SP the Original Game Boy? No—Here's the Lineage

No. The Game Boy Advance SP (2003) is a later revision within the Game Boy Advance family, not the original Game Boy.

The Game Boy Family Tree

• Original Game Boy (1989): "Brick" form factor, 2.6" monochrome (4-shade green) LCD, 4 AA batteries, link cable multiplayer. Iconic. Tetris pack-in.
• Game Boy Pocket (1996): Smaller, true B&W screen, 2 AAAs.
• Game Boy Light (1998, Japan only): Pocket + electroluminescent backlight.
• Game Boy Color (1998): Color TFT screen, backward compatible, 2 AAAs.
• Game Boy Advance (2001): Landscape orientation, 32-bit ARM7, 240×160 color (no backlight), 2 AAs. Successor to GBC.
• Game Boy Advance SP (2003): Clamshell redesign, front-lit (AGS-001) → backlit (AGS-101), rechargeable lithium-ion battery, same GBA internals.
• Game Boy Micro (2005): Tiny, horizontal, backlit, non-folding. Final GBA model.

The GBA SP is a refinement of the GBA, not the original 1989 brick. It's the most beloved GBA model thanks to the flip screen and rechargeable battery.