Walker is classic 2D shooter with the side-scrolling from the right to the left. Player takes control of gigantic robot AG-9 (codename Walker). The mission is simple - guide Walker through the four time zones and kill everybody/destroy everything. Every zone is also divided into two parts. The road is full of trained enemies with one single purpose - to destroy Walker. However, except relative immunity, the robot is equipped with twin 30mm carbines cannons. The number of enemies are actually huge, they are attacking in groups, off the ground and from the air. Also, every time zone consist of special types of enemies which force player to stay alert. As usual, there is a powerful boss at the end of level (luckily each boss has its own weak spot).
Until a couple of months before its release, the game was to feature two different types of levels, alternate levels being platform shooters. However, they decided that this section wasn't up to standard, and decided to stick to the basic shoot-em-up.
The game was ultimately in development for three or four years. The Walker project went into limbo for a year or two, during which time someone in DMA Design came up with the idea for Lemmings. Finally, Walker was released in 1993.
Scott Johnston rendered the head of the Walker using a small 3D program he wrote, to get all the different positions right. He then went in with a pixel drawing program to touch up the result.