Who are the best Pen and Ink Artists of all time?

I use to have a great hand at pen and ink and unfortunately I went to college and lost it. I just can't do it anymore. I would like to get back into it and would like to hear from you who are some of your favorite pen and ink artists of all time? I've been collecting Al Williamson and Milton Caniff works recently and I'm always looking for new influences. Thank you to all who answer.