Title: Evaluating and Inducing Personality in Pre-trained Language Models. Abstract: Originated as a philosophical quest, personality discerns how individuals differ from each other in terms of thinking, feeling, and behaving. Toward building social machines that work with humans on a daily basis, we are motivated to ask: (1) Do existing Large Language Models (LLMs) possess personalities, akin to their human counterparts? (2) If so, how can we evaluate them? (3) Further, given this evaluation framework, how can we induce a certain personality in a fully controllable fashion? To tackle these three questions, we propose the Machine Personality Inventory (MPI) dataset for evaluating the machine personality; MPI follows standardized personality tests, built upon the Big Five Personality Factors (Big Five) theory and personality assessment inventories. By evaluating models with MPI, we provide the first piece of evidence showing the existence of personality in LLMs. We further devise a Chain Prompting method to induce LLMs with a specific personality in a controllable manner, capable of producing diversified behaviors. We hope to shed light on future studies by adopting personality as the essential guide for various downstream tasks, building more human-like and in situ dialogue agents.