Stegosaurus by Heinrich Harder, a paleoartist active between 19th and 20th century. Note the spike arrangement on the tail: it's the Thagomizer!
The term "thagomizer" comes from a 1982 comic strip: the Far Side by Gary Larson. The strip shows a caveman professor discussing about the spikes on the tail of Stegosaurus. The professor explains to the audience that the spikes were named "after the late Thag Simmons" (Thag Simmons is a fictional caveman from Gary Larson's comic).
The paleontologist Ken Carpenter picked up the term and used it when describing a fossil at the Society of Vertebrate Paleontology Annual Meeting in 1993.
Thagomizer has since been adopted as an anatomical term!
The author of the comic strip has a background in Life Sciences, which explains his frequent use of animals and nature in the comic. For this reason too, he is well aware that dinosaurs and humans did not exist in the same era. Indeed he suggests that "there should be cartoon confessionals where we could go and say things like, 'Father, I have sinned – I have drawn dinosaurs and hominids together in the same cartoon.'"
The Thagomizer is not the only scientific term brought by comics. A nice example is given by a strip from "Calvin and Hobbes", criticizing the naming of the Big Bang as unevocative of the wonders behind it. The strip coined the term 'Horrendous Space Kablooie', which has achieved some popularity among the scientific community, particularly in informal discussion.
What about the suggested alternative to Tyrannosaurus rex, 'monstrous killer death lizard'?