G-Shock is a brand of watches manufactured by Casio, known for its resistance to shocks (e.g. hard knocks and strong vibrations).
Casio G-SHOCK DW-002
This is the first watch that I bought for myself and I remember it was around $250CAD at MACY's Vancouver, BC in 1994(??). It is very special to me. It came with dual strap option. On the strap it said USA Limited. You can see there are heavy wear on lower right of the case due to my first mountain bike experience. The battery actually lasted over 20+ years. (changed its battery the first time 6 month ago). An impressive tough G-SHOCK time piece.
Casio G-Shock
My first G-Shock, a gift from the wife in 1988. Model DW5600 (no letter). This watch has the threaded back, I had to order a special wrench to open it.