Spellfilcher
A Spellfilcher is a comparatively obscure concept for a multiclassed rogue/wizard, similar to the Arcane Trickster. It first debuted as an elfin kit in the days of Advanced Dungeons & Dragons, but later found a new expression as one of the "Age of Mortals" specific Prestige Classes for Dragonlance. It has currently fallen into obscurity compared to the Arcane Trickster.
The Elfin Spellfilcher
Appearing in the Complete Book of Elves, the Spellfilcher isn't as infamous as the Bladesinger only because gishes were always more popular than mage/thieves.
Lorewise, spellfilchers are elite elfin thieves trained from birth for a single goal: to pilfer spells, rare spell components, relics and other magical goods from the strongholds of wizards... especially the wizards of the non-elfin races. Organized into a powerful guild that demands their loyalty, spellfilchers specialize in using their magical affinity to detect and disarm magical traps. A similar organization is found in the form of the Collectors, which are an elite cadre of elfin Fighter/Mage/Thieves who specialize in retrieving lost elfin artefacts and relics from the hands of other races.
As a kit, spellfilchers gain Appraising, Spellcraft and Tightrope Walking as bonus nonweapon proficiencies, as well as the unique trait of a +5% bonus to their Find/Remove Traps skills when detecting or circumventing magical traps, which increases by a further +5% every four levels. Though they can't destroy such traps without the use of spells like Dispel magic, they can still make a successful Remove Traps check to disarm a magical trap for 1d4 + (1 per 3 levels) rounds. Aside from being restricted to the race and class combination of Elf Mage/Thief, there are no special requirements.
The drawbacks are all roleplaying centric: non-elfin wizards will hate and despise you, non-elfin thieves guilds will want to try and coax you into working for them, and you must remain loyal to the Spellfilcher's Guild or they will descend upon your head like a load of bricks.
In the Forgotten Realms, the Dark Seldarine god Vhaeraun is the patron deity of drow spellfilchers, who eagerly prey on non-drow elf wizards as well as other races.
The Krynnish Spellfilcher
In the Dragonlance setting, spellfilchers are much closer to the Arcane Tricksters of 5th edition. Appearing the "Age of Mortals" splatbook, spellfilchers are simply rogues who have some measure of magical talent, which they use to augment their thievery in various ways. They have a tendency towards flashy, flamboyant behavior. Most Krynnish spellfilchers are Rogues who have multiclassed with either the Sorcerer or Mystic, but there are Clerical and Wizardly spellfilchers as well, though they often need to juggle their thievery around the rules and strictures of their patron remple or order.
Becoming a Spellfilcher in 3e requires a Nonlawful alignment, a Reflex save bonus of +5, 6 ranks in the skills Bluff, Hide, Knowledge (arcana) and Spellcraft, the Silent Spell feat, the ability to cast 2nd level Arcane or Divine spells, and a Sneak Attack value of at least +2d6.
Aside from gaining increased spells per day/spells known at every odd-numbered level, the spellfilcher gains the powers of Spellwise (a Supernatural ability that lets them burn spell-slots to boost skill checks, sneak attack damage, Reflex saves, armor class and attack of opportunity accuracy, based on level) and Signature Spell (choose an iconic spell, which can be cast as a spell-like ability 1/day per even level in the prestige class).