The Chrysalis device was a piece of technology that, once activated by a triluminary, could genetically splice an individual's DNA with that of another species, making them a hybrid of the two. The outward extent of the transformation could vary - for example, Delenn became an obvious combination of human and Minbari traits, whereas Jeffrey Sinclair looked fully Minbari after the transformation (as Valen), while still retaining some human DNA, which he passed on to his descendants.
The process envelops the subject in a cocoon or chrysalis (hence the name) and can take several weeks to complete. At the end of which the subject "hatches" out of the chrysalis, typically in great pain and still covered by a brittle exo-epidermal skin that must be shed manually.
Considered a holy relic, the Minbari first obtained the device along with the three triluminaries from Valen during the First Shadow War. Valen had prophesied that when the Shadows returned to Z'ha'dum in a thousand years that a Minbari would use it to re-unite them with the other half of their soul in another war against the ancient enemy.
Delenn after receiving both it and the Triluminary spent from July of 2258 slowly assembling the device in her quarters on Babylon 5 before finally activating it at midnight on December 31st and emerged several weeks later as a human-Minbari hybrid.
The device originated from the Great Machine on Epsilon III and in 2260 it was brought back in time by Zathras aboard the White Star 1 to 2254, through the temporal rift in Sector 14. From there to Babylon 4 along with the Time-jump system that took the station a further thousand years back into the past and allowed Jeffrey Sinclair to become Valen.