Here are my three choices. Now that I've written them, I'm pretty much in love with all three of them, so go ahead and pick whatever seems to fit the group best.
Renard Foucault, expert on the Underdark, standing at the precipice of maddening revelation. (second from the left)
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Erwin Humboldt (far left), alchemist, mage, and mountebank. His motivations for venturing into the inky depths of the Underdark are largely financial. He took on a commission from a crime syndicate in Luskan to smuggle contraband arcane reagents down the Sword Coast and into Waterdeep. His crew ran afoul of the customs officials at Waterdeep, however, and they had to dump the cargo in the bay. Erwin's employers held him fiscally responsible. Now he's organized an expedition into one of the deadliest, most hostile environments in all of Faerun, because the alternative fate he'd meet at the hands of Luskan pirates is sure to be a whole lot worse.
Mechanically, he'd be a Wizard/Rogue/Arcane Trickster who sneak attacks with alchemical weapons and carries a bag of holding full of nasty surprises. He'd be a leader of sorts, but more of a scheming mastermind than a rallying hero.
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Cedric Tharkrash (far right), self-proclaimed hero of Calimshan, defender of Amn, and father (so he claims) of a hundred bastard children. Raised among humans by two half-orc parents in Calimport, Cedric effects a very gentile demeanor. He has been adventuring since his late teens, constantly hungry for fame and adventure. He cares little for material gain, pursuit of knowledge, the greater good, or other such temporary goals. No, Cedric has just one goal in mind: to be sung of by every bard, in every tavern, in every port, in every corner of the Realms. He figures a successful expedition into the deepest parts of the Underdark ought to get him halfway there.
He's definitely not a Barbarian, in my mind--this guy fights with a cool head. I'm imagining him using a sword-and-shield style that's heavy on shield bashing and movement. He might pick up some maneuvers from the Tome of Battle designed for two-weapon fighting, using the shield as an off-hand weapon. Definitely nothing overtly magical, but certainly flashy. His scimitar and shield are his most prized possessions, but he's also picked up a few trinkets that let him pull a surprise or two.
