Dr. Sloth is one of the oldest Neopets characters, dating back to basically since the site's inception. You can tell because he's from that era where the NPCs were just kind of Things—like, what is Sloth, exactly? Is he just an alien? A fucked up Chia? A male faerie? The answer is: Hey! Don't worry about it!

Being as old as the site itself, Sloth's design hasn't shifted too much all things considered. The basic elements were there from the beginning—green, three, uh, Things at the top of his head, black robes—but he looked especially skrunkly during this era and details would shift around at random. For example, sometimes he'd have liver spots, wrinkles, or would have either an undershirt or red cuffs to his robes.

Gradually, over time, Sloth's design got polished up as the art on the site just got better in general. His face got better definition, his robes got a red inside lining and a distinct upraised collar, and he stopped looking quote so wrinkled. Sometimes he would erroneously be depicted with sharp teeth (either as part of a full set of teeth or just as fangs) and having a blue tongue and/or claws.

After that, while his actual design elements didn't change much, his head shape got refined further, with a bigger smile and chin. The fangs and claws were lost completely in favor of a more humanoid appearance, and his eyes, while still red, gained pupils. This is, unsurprisingly, his best design/depiction, and the one most frequently used.

These design refinements also worked in tandem with the personality he gained over the years. Originally, Sloth was just a generic evil overlord type with no real personality whose only traits were being malicious and being responsible for like 90% of the conflicts on the site. As time went on, while he became no less evil or more well rounded, he did become delightfully hammy, with more of a love-to-hate personality, and his big grin and very expressive face really help to sell the idea.

Anyway I'm not sure what note to end on so I'm leaving everyone with this image of Sloth smoking a fat one that I found while looking for images for this review

Pros: kinda beefy NGL