Spencer is a tall, thin boy, with light brown hair combed back and big, sweet hazel eyes framed by the lenses of his glasses. He tends to dress in a way that mixes formal with informal, sometimes looking a little disheveled; untidy tie, dirty converse, oddly colored socks.

He's basically a nerd. He's the know-it-all of the group; 187 IQ and can read 20,000 words per minute. Despite being a genius, it is difficult for the rest of the police or agents to take him seriously, he is so young... so inexperienced and naive.

"Do you know why he always introduces me as Dr Reid?" Spencer asked Lula out of the blue, referring to the fact that Agent Gideon always introduced him to other people as 'Doctor Spencer Reid'.