A Transmuter is a form of Specialist Wizard in Dungeons & Dragons. These guys specialize in the school of Transmutation, the magical altering of physical substances and general shapeshifting shenanigans.
5th Edition's Arcane Tradition
Transmuters have a lot of fairly fluffy traits. Minor Alchemy (level 2) lets them temporarily transmuted a sample of of wood, stone, iron, copper or silver into one of the other elements on that little list. Transmuter's Stone (level 6) lets them spend 8 hours to create a magical stone. Whoever holds it gains a bonus chosen by the transmuter when making it; darkvision, +10 to speed whilst unencumbered, proficiency in Constitution saving throws, or resistance to one of five elemental damages (fire, ice, acid, lightning, thunder). Shapechanger (level 10) lets a transmuter turn into a Challenge Rating 1 or weaker Beast type creature whenever they want, plus they gain the Polymorph spell for free. Finally, at level 14, Master Transmuter allows them to destroy a created Transmuter's Stone to enact one of the following effects: transform one object into another object, completely heal (restore to full health + remove all curses, diseases and poisons) one creature, cast a free Raise Dead spell, or decrease a target's apparent age by 3D10 years.