Knightmare is a vertically scrolling shoot-em-up from Konami. It was published in 1986 for the MSX home computer. There were three Knightmare games, of which this is the first one.

The hero in the game is Popolon, a warrior on a quest to rescue the princess Aphrodite from the clutches of the evil priest Hudnos. Popolon must fight his way through waves of enemies and avoid being hit by their projectiles and obstacles. There are different levels, each with a boss monster at the end of the level, which must be defeated before continuing on to the next level.

Source: Wikipedia