Raziel is known almost entirely through a book attributed to him, which is the reverse of the usual direction in angelology. The name is built on raz, secret, and reads as the secret of God.
The legend attached to it is old and widely repeated: the angel gave Adam a book of heavenly knowledge after the expulsion from Eden, it passed to Noah, who is said to have built the ark by it, and eventually to Solomon. The book is presented as the original source of the whole tradition of practical wisdom, which is a claim about authority rather than a claim about a text.
Sefer Raziel HaMalakh, the work that actually circulates under the name, is a medieval Hebrew compilation drawing on earlier Hekhalot mysticism and on the late antique magical material of Sefer ha-Razim. It combines cosmology, angelology, the names and seals of angels and practical instructions, and it was printed at Amsterdam in 1701.
The printed edition then acquired a life of its own that had nothing to do with reading it. A copy in the house was held to protect the house from fire, so people who could not read a word of it kept one, and the book functioned as an amulet. Surviving copies with heavy wear on the binding and none on the pages are the physical record of that.
Chokmah, where the sephirotic table places him, is the first outflowing wisdom before it takes any form. Assigning the keeper of secrets to the sphere of undifferentiated wisdom is a legible choice by whoever built the table.