César de Bus (3 February 1544 – 15 April 1607) was a French Catholic priest and founder of two religious congregations.

At eighteen he joined the king's army and took part in the war against the Huguenots (members of the Protestant Reformed Church of France during the 16th and 17th centuries).

After the war he devoted some time to poetry and painting, but soon made up his mind to join the naval fleet which was then besieging La Rochelle, a seaport on the western French coast.

Up to this time, de Bus had led a pious and virtuous life which, however, during a sojourn of three years in Paris was exchanged for one of pleasure and dissipation.

Upon the death of his brother, a canon (priest) of Salon, he succeeded in obtaining the vacated church benefice (stipend), which he sought for the gratification of his worldly ambitions.