History
When Yinsen was about to operate on Tony Stark to put an electromagnet in his chest to save him from shrapnel approaching his heart, Stark refused salvation and, against Ho's will, activated a weapons-free "Rescue suit" for Yinsen to escape captivity. In his final words, Stark requested Yinsen to use the suit to rescue the world from people like him.
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Original suit given to Yinsen
Yinsen escaped the Afghan cave by deflecting bullets using the armor's abilities, and, on the way home, saved a DC-10 from crashing, discovering he could use this armor to protect the world as Rescue. Yinsen later improved the Rescue suit, and, at some point in time, he briefly fought the Defenders over a misunderstanding before eventually joining them, and expanding across the world, turning Earth into a "Defenders World."
In the present day, Yinsen was giving a speech commemorating the death of Tony Stark and the day he became Rescue.[1]