You can make any character within the branding, Marvel, DC, Star Wars, LoTR and so on, including videogames, merchandise, anyone in The Lego Movie or just an ordinary Lego person (As long as they have parts existing in Lego).
Yes, you make the mini figure of the character or existing person with existing parts. Like Lego Green Lantern, Lego Han Solo, Lego R2-D2, Lego Howard The Duck... anyone that has appeared in Lego form.