I Am Legend is written by Richard Matheson. Richard Matheson wrote Somewhere in Time
[Human]: Can you recommend a movie similar to I Am Legend? [Assistant]: I Am Legend is written by Richard Matheson. Matheson also wrote Somewhere In Time. [Human]: So is Somewhere in Time also a movie? [Assistant]: Yes, Somewhere in Time is also a movie. It is a travel and science fiction movie. Do either of those genres interest you? [Human]: Can you tell me who is in Somewhere In Time? 
William H. Macy, Teresa Wright, and George Wendt are the starring actors.