Mechanical would be the obvious choice. Hard to think of something more aligned to specific ‘codes’ (laws) than a robot, possibly clockwork.
Less obvious would be rectilinear quarried stone for its unyielding straight lines. Think the bot from Interstellar made of enchanted marble/obsidian.
You could also go for more of a literal interpretation in that they are formed of written laws on basically any material, written on paper for fast, vulnerable units, inscribed into stone for slow, resilient units, carved into the skin of corpses for a necromantic unit, etc.
Or take it in a more fluid direction by having them be akin to an air elemental, spoken into existence by legal decree.
My secret: all my characters are crazy. Sometimes it’s more obvious. (Fish-malk, best-malk!) Sometimes it’s more subtle. (What do you mean it’s not normal to pray to God so intensely you orgasm? I do it every day, privately.) None of them are sane. Don’t tell my players.