He doesn't care to work, reads poetry and initiates various creative projects.
He is the audience surrogate, allowing other characters to introduce themselves to him, and by extension, the viewer.
Ryan was hired to replace Tom Peets, an employee who had lost a battle with depression and committed suicide shortly before the start of the series.
As the series progresses, Ryan begins to display a great deal of contempt and disdain for both his coworkers and his job.
This becomes more apparent when Ryan is promoted in "The Job" to work at Dunder Mifflin's corporate office in New York.
In later seasons, several characters sarcastically use this term long after Ryan has risen to a more prominent position in the company.
Ryan is often the victim of Michael's antics and bizarre man-crush on him, usually resigning to requests without complaint.
Many of the staff, most notably Jim and Pam, note Ryan's ineptitude as an employee and that he sponges off his parents by living with them and driving his mom's car.
For the first episode and for much of season 1, Ryan's purpose in the show mirrors that of his British equivalent, Ricky Howard.
His downfall culminates in misleading Dunder-Mifflin's shareholders via his websites sales numbers, effectively committing fraud as Oscar Martinez later claims.
In Season 5 he returns with blonde highlights and a "work hard, play hard" attitude.
In the webisode "The Story of Subtle Sexuality", Ryan mentions that his parents live in separate houses, which implies that they are separated.