I just started at a advertisement company in Canada( i relocted from the states recently), i love my job and all it entails for the most part. When i started there was a coworker who trained me, my boss and all the employees get along with me and i feel free to say what i want when i want, i see this coworker as a mentor, he is the one that on a daily basis will email my work to me and i complete them, however  have come to find out that all the work he has been asking me to do, he is the one that is suppose to do them. infact just now he comes up to me and says he needs me to finish something because we are on a deadline and i know for a fact that HE IS THE ONE ON THE DEADLINE, i am not sure since i am so new if i should stand up to him, tell my boss or what. there are people who have been here for 3 years who have not stood up to him, all he does is stay on facebook and watch movies, granted i do the same thing but i do my work, i should not be responsible to do his work, i decided today that i will not finish his deadline and when he comes to work on Monday i will just say it was too much for me.

You say you are new, for the sake of your job tread softly.

If you are VERY sure about your discovery,let him know that you know.I doubt if he will continue with his gimmick.