Iron Fist

Iron Fist is a perk in Fallout 3 and Fallout 4.

Effects
Each time this perk is taken, it increases Unarmed damage by +5 points.

Bugs
Upon unlocking rank five, critical hits in V.A.T.S. while wearing power armor will no longer function; the Sole Survivor will simply stand idle while no animation is played or AP is consumed.

Behind the scenes
The perk is a reference to the Marvel Comics character Iron Fist, whose chi-focusing abilities allow for powerful punches and attacks. This is further proven by the Fallout 4 version carrying the description,

Eisenfaust Puño de Hierro Poing de Fer (Compétence) Стальной кулак Сталевий кулак