John Krämer (known also as Institor, a Latin form of his surname) was a German Carthusian writer.
In the first part the author teaches a good religious divers means and practices which he should observe in order to remain a faithful Christian, to acquire, on earth, the grace of perfection and, in heaven, ever-lasting happiness.
In the second part, by a quaint allegory, he puts the religious on his guard against the faults of monastic life which are represented by twenty birds of prey, the eagle, the vulture, the hawk, the owl, etc., whose characteristics and manners he describes.
The subject of Krämer's second book is against anger, as indicated by its title, "Tractatus exhortativus ad evitandam malam iram".
An unpublished treatise, "De Objectionibus bibliae", has also been sometimes attributed to Krämer, but without sufficient warrant.