Date of Birth: 17 June 1985.
Juhani Otso Berg was born in Mikkeli, Finland, but was dragged around the world by his father, who worked for an oil company belonging to one of Abstergo's many subsidiaries. So young Master Berg was raised by rig pigs in Afghanistan, Kurdistan, and Oman, to name a few. And that doesn't really sound like a magical childhood, does it?
With his father's blessing, Berg returned to Finland to join the army. At first, they made fun of his muddled accent (technically speaking, he doesn't even pronounce his own name correctly) but the jokes quickly stopped as Berg proved himself to be an exceptional recruit, becoming one of the youngest Special Jaeger in the Utti Jaeger Regiment.
He met his wife Helmi in the army, and everything pointed to an intense, but unremarkable life, until his daughter Elina was born and diagnosed with cystic fibrosis. While Finland's health care system is generally considered to be quite good, the Berg family found themselves struggling to afford the aggressive drug treatments Elina so desperately needed.
Berg quit the army and became a well-paid mercenary, which his wife did not approve of, resulting in divorce. It's not exactly a doctor or a lawyer, is it? Berg's freelance activities caught the attention of Dr. Warren Vidic, who recruited him into Abstergo's Animi Training Program in exchange for an off-the-market miracle cure. I imagine Berg's divorce became much more amicable (though not less final) after that.
Just as he did in the army, Berg showed promise early on and quickly rose through the ranks, and eventually won a spot in the Inner Sanctum of the Templar Order. He was given command of Sigma Team, an elite force designed to hunt Assassins. He's been a pain in the proverbial balls ever since.
(TL;DR: Otso Berg is a scary motherfucker and someone actually made a baby with him! GROSS -RC)