Timbuk2, the San Francisco-based firm best known for its customizable messenger bags, has announced that its chief executive, Mike Wallenfels, has resigned. The position will be covered by Ken Pucker, the company's board chairman, until a replacement is found. Wallenfels, who will continue to work with Timbuk2's board of directors and senior management through the end of March, is said to want to pursue personal adventures and work as an independent consultant for outdoor-related companies. He joined Timbuk2 in 2009 from Mountain Hardwear Inc., where he also held the position of chief executive. Timbuk2 recently announced plans to open stores in Denver and Chicago this spring.