PLESSYS, or PLESSIS, Pacificus du, French missionary, born in France in the latter part of the 16th century ; died in Quebec in the first part of the 17th. He was one of the four Recollet missionaries that accompanied Champlain to Canada in 1615, and was employed to instruct the children of the French and Indians that had settled at Three Rivers. His influence over the Indians enabled him to render a great service to the French colony. In 1618 a conspiracy was formed to cut off all the French, and 800 Indians assembled near Three Rivers to carry out the plot. Brother Pacificus was warned by a friendly savage. He gained over some of the chiefs, and with their help prevailed on the others to agree to a treaty of peace, which he undertook to negotiate with Champlain. He sailed with the latter for France the same year, but afterward returned to Canada. His body was discovered near the vault of Champlain in 1866.