Agent-oriented models are frequently used in disciplines such as requirements engineering and organizational process modelling. i* is currently one of the most widespread notations used for this purpose. Due to its strategic nature, instead of a single definition, there exist several versions and variants, often not totally defined and even contradictory. In this paper we present a comparative study of the three most widespread i* variants: Eric Yu’s seminal proposal, the Goal-oriented Requirement Language (GRL) and the language used in the TROPOS method. Next, we propose a generic conceptual model to be used as reference framework of these three variants and we show its use for generating specific models for the three mentioned variants, as well as for other existing proposals.