This paper proposes a critical approach to and reasoning on the connection between notions and practices related to masks, avatars and humans, attempting to find out about and understand their functions and developments in contemporary technoculture. Masks and avatars have many features in common, both are notions created by oral cultures with a strong religious meaning which have changed over the years, becoming part of leisure activities in daily life. At the beginning of 20th century, Sigmund Freud said human beings were a kind of Prosthetic God and in the 1960s Marshall McLuhan coined the idea of technology as an extension of the human body. Nowadays, in a mobile, networked and digital society, humans should be defined not only as the users of prostheses, but also as prostheses controlled by an avatar in multi-user virtual environments like Second Life, There and World of Warcraft. Our hypothesis assumes that contemporary avatars, in the field of computer sciences, are prostheses that include and replace the early notion of mask, coined in theatre and literature, transforming the way we interact and think about ourselves.