Data is a unique character although he does have an almost identical brother. Unlike the rest of the crew on the Enterprise, Data is not human but an android. The only android Star Fleet has that is centient.
Data is good friends with Geordi and struggles to come to terms with human feelings and actions. However his "father" who created him built him an emotion chip. This was eventually activated for him by the time of First Contact.
Data's brother named Lore, originally possesed the emotion chip however Data took it when Lore was dismanteled in the episode Decent part II.