DOOM: 17 Easter Eggs, Secrets & References You Must Find

3. Helmet & Dopefish - Commander Keen

Talk about knowing where you come from. Commander Keen was iD Software's first game, way back in 1991. Following the titular character, only a handful of retro-lovers will remember the plinky-plonk charms of the side-scrolling platformer.

This marks the second time the character has been paid tribute, having appeared at the close of DOOM II in 1994. Sadly it's not aged as well as something like Super Mario Bros., but is still a fantastic nostalgic nod all the same.

In addition to this, a legendary meme that spawned from another Commander Keen character, Dopefish, can also be spotted as you're roaming around. Located between two joining walls, the shape is an exact up-res of the 90s original.