Your costume suggestion
You wear the formal chauffeur’s uniform of grey suit and cap but have (fuel) injected it with driving gloves, moustache and aviator sunglasses. And your lucky fluffy dice, of course.
Growing up poor had its drawbacks. For a start, your dream of being a top racing driver was hampered by the availability of cars - nobody in your family had one. So you became a BMX demon and rode everywhere doing stunts. One day, during your 2000-drop paper round Lord Heathcliff saw you perfecting some triple endos and invited you in to see his eighteen car garage. When he offered you the job of cleaning them you accepted on the spot, and slowly worked your way up to become his chauffeur.
INTRODUCE YOURSELF AT THE START OF THE GAME BY READING THIS
I’m Lord Heathcliff’s chauffeur, Ford Escort. It’s a pretty boring job, so at the weekends I race for a Formula 3 team and they’ve just offered me a permanent position. When I’m not behind the wheel I’m usually getting paid to have dinner with nice ladies. I can’t remember exactly where I was when Lord Heathcliff was killed but I was definitely in the manor somewhere. I don’t see why I’m a suspect though, I’d just handed in my resignation.