The significance of the study consists in describing and enlarging the concept “penitentiary criminal in places of detention” as well as determining the impact of the criminal’s environment on his / her personality and behaviour. The paper analyses the identity of the penitentiary criminal and identifies his / her illegal actions in relation to the administration of penal colonies. The purpose of this study is to analyse a criminal who is in prison and has committed violent crimes against the staff of penitentiary institutions. In the article, the author uses the following methods of research: empirical (observation, description) and theoretical (analysis, questionnaires, generalisations). The content of the study is based on the information about the criminal. The article sets out the necessary criteria for investigation the identity of the criminal. The factors influencing the development of criminal’s personality and his / her behaviour have been defined. The informal levels of control are conditionally divided into three types as follows: highest, intermediate and lowest. The highest level is the elite managerial one. It is headed by the «thief-in-law» (code-bound thief), and if there is not any – by the «watcher» (criminal kingpin). The intermediate level is made up of «men» (PIs – Prison Industries), i.e. people who work in prison, although they may not work. The lowest level is represented by the «offended» (punks), morally and physically humiliated people. The author examines socio-demographic (social origin and status, marital and job status, level of material welfare, nationality, gender, age); psychological (emotions and will); criminal-legal and social role-related characteristics of the convicts who have committed violent crimes against the staff of penitentiary institutions. The author assumes that a socio-demographic characteristic of criminal’s personality is one of the most important existing ones demonstrated by the criminals who have committed violent crimes against the staff of penitentiary institutions. Age is one of its indicators. Social status is one of the most important indicators that characterises the identity of the criminal. These data show in which social strata and groups, in which spheres of public life and production, certain crimes are most common. The results indicate that a deep and comprehensive study of the identity of the criminal will increase personal safety of the staff of penal colonies and will allow both reacting more quickly and preventing a crime.