Short answers, pulled from the story.
Eric Northman was a Viking man deemed an adult at age twelve who married Aude, his brother's widow, when he was sixteen. He had six children with her, but only three survived until he turned into a vampire in his early twenties.
A Roman vampire named Appius Livius Ocella ambushed and turned Eric Northman one night while he was in his early twenties. His first name comes from Old Norse meaning One ruler or eternal ruler, and his last name means man from the north reflecting people who spoke Old Norse in Sweden, Norway and Denmark.
Eric Northman stands approximately six-foot-four with long blonde hair that Pam cuts shorter after blood gets in it during the first season. He wears dark blue jeans with a black singlet and a black leather jacket throughout the series.
Eric Northman serves as Sheriff of Area Five which covers northern Louisiana including Bon Temps. He owns Fangtasia, a vampire bar in Shreveport that acts as his headquarters where he runs operations with help from his progeny Pam and underlings.
Sookie Stackhouse and Eric Northman consummate their relationship after being wed by vampire laws in book nine Dead and Gone. They exchange a ceremonial knife given to Sookie by Eric which signifies they are pledged to one another according to King Felipe de Castro's representative.