History of Challenger

Challenger is a triumph whose game text reads: complete weekly challenges throughout the system.

How to complete

The exact count, season and seal were not confirmed by any source I could open (Destinypedia's triumph list and the seal guides I checked do not list it). Weekly challenges are the time-limited triumphs that unlock each week of a season (see Seasonal Challenges); TheGamer describes how they work. Completing those is the likely route, but that is unconfirmed.