Lancelotto Politi (religious name Ambrosius Catharinus, 1483–1553) was an Italian Dominican canon lawyer, theologian and bishop.
The 1913 Catholic Encyclopedia describes Catharinus as a "brilliant eccentric", and asserts that, despite frequent accusations of heresy, his teachings were always "within the bounds of orthodoxy".
This may account for his independence, and his defence of opinions which were singular, especially in regard to predestination, the certitude of possessing grace, the residence of bishops in their dioceses, and the intention required in the minister of a sacrament.
He was a strenuous defender of Catholicism against Martin Luther and his followers; and was prominent in the discussions of the Council of Trent, to which he was called by his former pupil, Cardinal del Monte, legate of Paul III.
In the third, public, session (4 February 1546), Catharinus, pronounced a notable discourse, later published ["Oratio ad Patres Conc.