He is usually depicted as a young man who works as a cub reporter and photographer for The Daily Planet, usually in conjunction with Lois Lane and Clark Kent whom he idolizes as his ideals for his career ambitions.
He is also known as Superman's pal and has privileged access to him with the aid of a special signal watch which emits a special ultrasonic frequency signal which Superman can hear anywhere on Earth. He also goes by the nickname, "Mr. Action" and in the silver age occasionally took a potion which gave him stretching powers as Elastic Lad.
During the Silver age, the character starred in his own comic book, Superman's Pal Jimmy Olsen, which featured his various adventures with and without Superman. It was generally regarded as a poorly written subsidiary title by both readers and creative staff. The most notable period was in the early 1970s when the singular artist, Jack Kirby, took over the title and created his own distinctive stories as part of The Fourth World which introduced many addtions to the DC Universe including the supervillain, Darkseid.
The character has appeared in every major filmed adaptation of Superman.