Thesis advisor: Donald Cox / Does a CEO’s narcissism influence the company’s stock? Would it matter if it is a media company? The Efficient Market Hypothesis claims that it matters little given market efficiency, as narcissism has been priced in stock based on the Capital Asset Pricing Model. Existing literature is divided on whether CEO narcissism influences corporate efficiency. This paper refines assumptions on asset pricing by indicating when market inefficiency occurs through panel studies, which the Adaptative Market Hypothesis overlooks. A case study on Elon Musk suggests that the CEO’s narcissism with media involvement creates temporary market inefficiency. This paper innovatively combines an event study of Elon Musk's Twitter activities on Tesla and Twitter with a panel analysis of 17 S&P 500 CEOs. The finding shows that younger and female CEOs, who derive narcissism supply and lead media companies, are more inclined to take risks on stock returns. This result suggests re-evaluating stock market efficiency to include CEO demographics and personality, which extends beyond traditional CAPM models. / Thesis (BA) — Boston College, 2024. / Submitted to: Boston College. Morrissey School of Arts and Sciences. / Discipline: Economics. / Discipline: Departmental Honors.