Jim Halpert
Jim excels at pulling pranks on Dwight, his annoying as
hell co-worker. Some of his pranks include putting his calculator in Jell-O,
sending him faxes from himself from the future (using a box of his stationary),
and dressing up like him, complete with a signature bobble head doll. One of his
more creative stunts was weighing 
down his headset with nickels so that Dwight
got used to the weight of it, and then when he removed them, he hit himself in
the head when he answered the phone. After a while, Jim realized that these pranks were childish, but he still
indulges them.
On the serious side, Jim transferred to the Stanford branch when it was too
painful for him to be around Pam, the receptionist who he had been in love with
for 3 years. However, just as the Stanford branch was about to absorb Scranton,
the manager at 
Stanford told Dunder Mifflin's brass that he had leveraged his
new position into a senior management role with Staples. Jim was thus
transferred back to Scranton, and back subsequently told Pam he loved her. He
did kiss her, but at the time, she was engaged to Roy, the warehouse worker. When Roy found out that Jim had kissed Pam one night, he tried to punch him at
work. Of course, Dwight, who keeps weapons hidden ALL over the office, used his
pepper spray to utterly and completely incapacitate him. 
Pam and Jim finally got
together, although it did lead to the exit of another worker, Karen Filipelli,
who had moved from Stanford to be with Jim. Her bitterness was made evident in
season 5, when Jim, Dwight, and Michael trashed Karen's industrial copy machine
in retaliation for her trying to poach the number 1 salesman at Scranton,
Stanley Hudson.
Jim became the number 2 at Dunder Mifflin following the merger of the Scranton and Stanford branches. While goofballs Dwight and Andy are now jockeying for the number 3 positions, Jim bought his parent's house as a surprise for Pam, and that's where the series stands right now.