- "The Thinking Cap... I'm gonna help you finish the Thinking Cap."
- "It's an Intelligence Booster, actually. It's got an intelligence boost."
- —Cisco Ramon and Harry Wells[src]
The Thinking Cap is a device conceptualized by Clifford DeVoe and built by Marlize DeVoe to help make the former smarter. A modified version, nicknamed "Death Cap" by Cisco Ramon or "Intelligence Booster" by Harry Wells, was developed by the two of them in order to bring Harry's mind to the same level as DeVoe's in an attempt to get ahead of him.
Wishing to enlighten his students' minds, but unable to execute his plan, Clifford DeVoe designed the concept for a piece of technology he described as his "thinking cap", a device that would allow a human to use the full capacity of their brain. He requested that his wife, Marlize DeVoe, create it for him, citing her expertise in mechanical engineering.
On the night of January 7, 2014, the couple attended the public unveiling of the S.T.A.R. Labs particle accelerator. Anticipating the failure of the accelerator's design and subsequent explosion, the duo hoped to siphon the excess energy to power their device and remained on the premises following the conference. As the accelerator exploded, DeVoe stood in the rain whilst wearing the Cap, allowing it to absorb numerous bolts of lightning generated by the accelerator. Coupled with the release of dark matter from the particle accelerator's explosion, DeVoe was transformed into a meta-human wielding a highly enhanced intelligence.
A second version was (reluctantly) built by Cisco Ramon at the insistence of Harry Wells as a way to better combat DeVoe. Cisco was worried over the long-term effects it would have on the user, aware that the original Cap tainted DeVoe's mind, and originally, body. On Cisco's orders, Harry altered his design to operate to reduced capacity without the introduction of dark matter. Despite multiple setbacks, including setting itself on fire, Harry got his Thinking Cap to work. He used it to teach Iris West-Allen to make a tidal wave while empowered with Barry Allen's abilities and learn the names of the last two bus-metas: Janet Petty and Edwin Gauss.
However, Harry wasn't satisfied, becoming addicted to using the helmet. His usage of the Cap escalated over time, commonly integrating it in his daily life for menial tasks, such as learning how to make the perfect pancake. Concerned for his well-being, Joe West hid it from Harry, causing the latter to erupt into a frenzy after confronting Cisco about hiding it. His maniacal and atypical behavior alerted them all, bringing Joe to compare it to Francine's drug addiction. This dissuasion was effective, but non-permanent. Obsessed with stopping DeVoe, Harry tried to charge the Cap with dark matter. The process worked temporarily, but came with a devastating side effect. As confirmed by Gideon in the Time Vault, Harry's intelligence was actually decreasing at an unknown rate due to the catastrophic death of his neurons. Ashamed, Harry initially hid his condition from everyone, but eventually later confessed to Cisco after destroying a similar Cap designed for him.
Behind the scenes
- In the DC comics, the Thinking Cap was the main source of the Thinker's abilities, which included telekinesis and mind control.
- While the cap never gave Clifford the ability to control minds like in the comics, Dominic Lanse's powers were eventually able to do something similar.