According to the Oxford English Dictionary,

This word has long had taboo status, and for many speakers constituted the strongest expletive available. This is reflected in the regularity with which dashes, asterisks, etc., were formerly used to represent the word in print, and in the large number of euphemistic forms to which it has given rise, including bee n.3, bleeding adj. 5, blerry adj., plurry adj., sanguinary adj. 4, and perhaps blooming adj. 4. In the case of the adverb, the considerable public reaction to the utterance of the word on the London stage in George Bernard Shaw's play Pygmalion in 1914 (see quot. 1914 at sense C. 2b) gave rise to the further humorous euphemism Pygmalion adv. In most contexts the word's taboo status has now been largely or entirely lost; the process of normalization seems to have begun earliest in Australia.

It appears that the use as an intensifier has existed since the 16th century and gained currency toward the end of the 17th.

Various interpretations of why it came to be (although no consensus appears to be reached) include the hot temperament associated with young noblemen (colloquially called bloods, after what was considered a hot-tempered humor in the early modern English period), associations with the Eucharist (wine was the blood of Christ and 'bloody drunk' appears to be our earliest known usage of the term as an intensifier), and the swear word "'Sblood!" a common reference that arose from "his blood!" i.e. Jesus' blood ('zounds!' is a contraction of 'his wounds!' in a similar vein). Alternatively it may have just been used in terms of various despicable peoples (bloody whore, bloody murderer, bloody villain) in reference to the actual bloodshed they caused (bloody whore as a reference to the Whore of Bablyon) which later turned into an all-purpose intensifier.

/r/etymology might be able to help with this question.