The first decan of Leo covers 0° to 10° of the sign. Firmicus Maternus gives its face ruler, in the Chaldean order, as Saturn, while Leo's domicile lord, the planet that rules the sign, is the Sun. Chaldean order runs through the seven visible planets from slowest to fastest, and this decan falls to the slowest, Saturn. Medieval authors rank a face as the lowest of the five dignities. Saturn is in detriment in Leo, a concept the tradition names explicitly only late, so the face ruler has weak standing in the sign itself. Saturn is also a malefic, a planet the tradition treats as difficult in nature. It shares the Sun's day team under sect, the tradition's sorting of planets into day and night teams. Leo is a masculine, fixed fire sign. Later practice reads the face after the major dignities, not instead of them.
A note on “detriment”: the early Hellenistic texts note a planet opposite its own sign without naming it. The term is defined only in late and medieval sources, and scholars disagree on whether the idea was implicit earlier.