Michael O’Hare was pretty healthy when they filmed the pilot, but got worse after, which is part of why season 1 was delayed; he took some time for treatment and JMS held off on filming until he was ready to come back. He took a turn while they were filming the season and it affected his acting. He came back for a guest appearance later on when he was feeling better and put in his best performance as the character. He retired shortly after, though.