Insofar as this can be considered a "study", HAH! I'm just bored. Again.
Being the very first AGI character, and wearing red to boot, it didn't seem too weird to draw the original Graham with a yellow skintone... if most other characters in the very first game didn't have the customary red skintone! And that makes KQ4 the only AGI game where Graham isn't severely jaundiced. There's a nice bit of consistency regarding Graham's gray hair, though it's hard to tell without looking at his talker portrait. Unfortunately, Graham barely appears in KQ6 and doesn't seem to appear at all in KQ7 so all you get is this one frame from the ending.
LSL1-AGI's Larry actually looks more cartoony than most AGI sprites, with a different head on the same basic cycle. Like SQ3's Roger, the LSL2 Larry is mostly an upgrade on its predecessor, but with a noticable and plot-relevant receding hairline. LSL3 on the other hand did away with the cartoony look almost entirely, only to be restored in full force with interest on top for the later games and the LSL1 remake. Not shown here is the chronologically-consistent lack of a bald spot on the LSL1 and 3 sprites. The LSL6 SVGA update's sprites are mostly upscaled by automated filters, but important things have manual tweaks.
I'll never quite get over one thing regarding Passionate Patti. Not the thing where her dress is blue in the EGA version of LSL5, that's obviously because of palette limitations, but the fact that she's drawn in a more realistic style compared to cartoony Larry. Shades of Roger Rabbit...
SQ3's Roger, being early SCI, looks much like a higher-res take on the AGI sprites, much like Larry and Rosella in LSL2 and KQ4. Also, most SQ games have Roger in the same outfit — he wears a few different ones in SQ1 (both versions) and two differently-colored Starcon uniforms in SQ5. The red Starcon uniform appears in SQ6's intro movie as well. A patch has recently been released that corrects Roger's hair color in the AGI games to blond and changes his SQ1 uniform for consistency, among other things.