I imagine my being a gearhead was hereditary as my adoptive parents considered cars appliances but my biological father was apparently an auto mechanic. Big shock finding that one out.
As far as cars that got me hooked, well, I was born hooked. Though the first car I remember my Dad having was a '71 Maverick Grabber 4-speed, it was just Dad's car--"the Red Bomb" as the family affectionally knew it. By '76 it was so rusty you could chuck a cat through it with the windows up. At the same time, Mom had a '69 Polara tow-package car with a K-code 440 and 3.55SG that would probably hand the Mav its ass.
The Mopar thing started with that wagon, since I spent a lot more time in that car than the Grabber, as well as my all-time favorite Hot Wheel which belonged to my godmother's son. It was a '67 Barracuda fastback with the redline wheels... I loved it and it was the only toy car I ever treated with respect.
However, the first two cars I ever remember seeing that really blew me away were a Guards Red Porsche 911 and a Vitamin C Superbird owned by someone that worked at the local discount store.
Anyhow, by the time I'd gotten old enough to really know about cars, I found out that there were a few gems in the family past. My Dad's first car was a 1955 Chevy 150 or 210 coupe with a 265 Power Pac and a 3-speed. He owned it for two weeks; his parents flew down to Virginia, picked it up and drove it home when the Corps sent him to Okinawa. Mom threw out the receipt for that car not long after Dad died.
My uncle (Dad's brother) had a four-speed '61 Pontiac wagon with either a 389 or 421. The champ, though, was Grandpa's Dodge, which my parents took on their honeymoon: a bright-red 1957 Coronet D-500 with the pushbutton auto (there's a funny story about that pushbutton...). Sadly, by the time I came along, both Grandpa and the Dodge were long gone but that car rouses a lot of memories among my uncles, usually prefaced by "That car was way too fast for Dad."
What really cemented the already-Mopar-slanted fetish was my friend Dave buying a '74 'Cuda when he was 14. We worked on that car for nearly 3 years before ever legally driving it, but Dave lived out of the way and there were a number of not-old-enough-to-drive back-road hijinks well before that.
So, though I couldn't find a Mopar for my first ride, when that one died of a broken back, I found a '73 Challenger 340/4-speed car that forever sealed my fate. I've been sidetracked a time or two, but it's been Pentastar power for the most part ever since.