Claes Reimerthi (born January 12, 1955 in Ystad) is a Swedish comic writer, having worked with characters such as The Phantom and Bamse. Reimerthi has written more than 100 stories about The Phantom and is a member of Team Fantomen, the Swedish "braintrust" that set the line of what is going to happen to The Phantom.
During the 1980s he primarily used the pseudonym Michael Tierres for his work, and periodically he has also used Frans Möller.