Rip Hunter... Time Master, a Silver Age hero who made his debut in Showcase #20 (June, 1959) on the heels of The Challengers Of The Unknown success story. Written by Jack Miller and illustrated by artist Ruben Moriera, the Pre-Crisis Time Masters group consisted of Bonnie Baxter, Corkey Baxter, Jeffery Smith, and Rip Hunter, and Time was an adventure, but then came Crisis on Infinite Earths and that history was wiped clean.
Then came the resurrection of Dr. Ripley Hunter when he was called in to save Booster Gold from a deadly disease only treatable in the 25th Century. Soon after Rip got his own 8 issue mini-series which introduced the dreaded and controversial time-travel limitations. This involves the fact that any method of time-travel can be used only once per person, because of the fact that the stress on the body is too much for normal humans. The Time Masters mini-series also made use of some of the little used DC Universe heroes like Cave Carson, Doc Magnus, Dan Hunter, and Arion. Time Masters also gave us a historical cameo filled look at the DC Universe with the Immortal Vandal Savage and the Illuminati as the villains. There were plans for a sequel to Time Masters, but those plans were canned long ago.
A well-known fact is that Rip Hunter is a member of the time spanning "Time Police", otherwise known as The Linear Men, who have there base of operations at Vanishing Point. 'Hunter' has averted time-stream disasters for countless time-lines. But, Hunter's exact origins remain a mystery, as do his recent connections with the pre-crisis Rip Hunter...Time Master.
To further make things interesting. Because of Zero Hour the time stream has been severely altered making countless Reboots, Unboots, Births, and Deaths too mean nothing to the greater picture which is Hypertime. The Challengers of The Unknown, Zatanna, Doomsday, Rip Hunter and countless other's pasts have been so severly altered that they are now a part of Hypertime's infinite parallel time-lines, destined to be lost forever.