'Martin Frobisher' was the first Explorer rose.

[From Gardening with Roses, by Judith McKeon, p. 34:] The Kordes rose was... used in breeding Canadian Explorer roses at Agriculture Canada in Ottawa; they offer extreme hardiness and repeat-flowering in shades of deep pink and crimson... hardy to Zone 3.

[From Peter Schneider on Roses, p. 149:] Many of the explorer roses are several generations removed from their ugosas roots and lack essential characterisitics of the class.