Regarding purely role-playing elements, they are just fluffs. Your Knight can be of any background and personality.
But mechanically, a Knight as a build is still a defender. It's class features and powers are focused on protecting others. If that is OK, just make a Knight and call it in any name. Your Knight maybe truly a honorable Knight, or an outlaw fighter who is just good at fighting alongside some other gangs.
If that is not what you want, and you want to make a striker, whom simply continue to strike opponents until they die (melee striker) .... well, if I were you, I will talk to the DM and use all the rules regarding Slayer, including that using two-handed weapon by the rule, but describe that he is using sword and shield.
By the rule, your fighter is using a, say, Fullblade. Regarding all the rules, It works as if he is only using one two-handed weapon. Your [W] is 1d12. You don't gain any benefit from that imaginary shield. Maybe you can use your "shield hand" as easily as a combatant who has only one big weapon. But in your fantasy world, he looks like having a big one-handed weapon and a shield.
Actually, the game designers and DMs are doing nearly the same thing for monsters. A monster's damage and defenses are based on their level and role, not on their gears.