What to say about Dwight? Co-owner with his cousin Mose of a beet farm in Pennsylvania, Dwight is also the star salesman at Dunder Mifflin. Coming from a weird Amish family with links to Nazi Germany (he tried to visit his Nazi war criminal grandfather in Argentina, but some Jewish groups protested his being issued a visa), Dwight is a constant thorn in the side to Jim, who he sits with, although there is a begruding respect between the two... just barely.
Dwight loves collector items, such as bobblehead dolls, and other sci-fi stuff (laser tag, Battlestar Galactica, and The Lord of the Rings. He's also notoriously inconsiderate and selfish, yet at the same time, extremely hardworking and dedicated to Michael Scott. In the beginning of the series, he was ranked as "Assistant to the Regional Manager", although he liked to say "Assistant Regional Manager" (after which Michael, being a jerk, would correct him).
After Jan yelled at Michael for having Movie Mondays (half hour segments that
increased productivity, because, as Michael said, "they have to work harder to
catch up on the work they missed"), Angela, with whom Dwight was having an
intimate relationship, encouraged him to approach Jan and ask her to give him
the branch. Jan initially agreed to mull it over, but instead told Michael.
Michael, in turn, pretended to be demoted by Jan and gave command of the branch
to Dwight, until he decided to trade in his company lease, a convertible Sebring
("a ridiculous choice in this climate", according to Dwight). Suffice to say,
Michael lost it, and punished Dwight by making him wear a 
large sign that said
"liar" and he had to do Michael's laundry for a year.
When Andy came over from the Stanford Branch, he learned of Dwight's attempted takeover, and leveraged it to raise suspicions about Dwight being late one morning (he had gone to New York to turn in some Accounting work that Angela forgot to turn in). Rather than confess his love for Angela and turn them into the office pariahs, Dwight quit. Over the next several weeks, Andy tried to become Michael's friend, but instead, ended up annoying him, and when Jim hid his cell phone in the ceiling, he lost it and punched the wall. Michael then went to ask Dwight to return from Staples, and he did.
Dwight eventually mercy killed Angela's cat, who was suffering from almost EVERYTHING a cat can suffer. During the Michael Scott Cure for Rabies Run (he hit Meredith with his car, and in the hospital, it was discovered that she had contracted rabies when Dwight trapped a bat in a plastic bag over her head), Angela found out about the cat and broke up with Dwight, saying she couldn't look at him anymore. Instead, she started dating Andy, and eventually got engaged to him. Dwight's pain was initially intense, but after Andy's eagerness in wedding planning started to get to Angela, she began paging Dwight for trysts in the warehourse (which, to Dwight's delight, was quite often). The last we heard, Dwight will be showing Schrute Farms to Andy and Angela for their wedding, but he hasn't given up on trying to win her back...