The "Whyman" is the name Ryusui gives to the source of powerful radio wave messages the Kingdom of Science receives after the creation of the antennae. The name is chosen as the messages consist only out of the repeated word "why" in Morse code.
The "Whyman" is the main antagonist of Dr. Stone.
The true nature of the Whyman is currently unknown.
For unknown reasons, Whyman attempted to petrify humanity again with attempted usage of petrification device.
Age of Exploration Arc
The Whyman is first heard being heard on the Kingdom of Science sonar on the motorboat. Whyman consistently yelled, "Why".
Determining the nature of the Whyman is a major goal of the Source of the Petrification Saga.
Treasure Island Arc
After the conflict on Treasure Island is done, a signal takes over the radio in an attempt to activate the petrification device, with the distance being Earth's diameter and the time 1 second. This call has the Kingdom of Science confirm that Whyman is a villain. It is unknown if the two signals were from the same source. However, the voice, as noted by Ukyo is the same voice as Senku.
The source of the Whyman's transmissions is apparently on the Moon.
New America City Arc
The Kingdom of Science decides to travel the world and gather supplies for space travel to confront the Whyman. Some members want answers while others, like Matsukaze, want revenge.