See the plot of Tron (1982) below for a concise detail about the said movie:
Kevin Flynn (Jeff Bridges) is a young and gifted software engineer. He was once an employee of the software corporation ENCOM, and had developed several video games after hours to start his own company. However, a co-worker, Ed Dillinger (David Warner) took Flynn's code and presented it as his own, eventually earning him a series of executive promotions to become the company's CEO. Flynn, meanwhile, was terminated and reduced to running a video game arcade, which ironically featured several of the games he had created. - read more at Wikipedia.org.
So if you are a die hard Tron fan or just want to know where the Tron: Legacy all started, then you should watch Tron now. By the way, when I saw this film I am really amazed how they make use of the 3D special effect back in the 80s but of course you'll see a big difference if you'll compare the current Tron.