Bramimond

Bramimond the Enigma is a hermit that sleeps beneath the Shrine of Seals in Bern, and was one of the Eight Legends who fought in The Scouring, wielding his dark tome Apocalypse, the Silencing Darkness.

Though Bramimond was originally male, due to his perfect mastery of dark magic, he no longer has any specific gender or personality, instead mirroring the personality and voice of the person speaking to them. Because of this, the Bramimond that is seen in his picture is how the Tactician views him. With Eliwood, he is reserved, with Lyndis, he is resolute, and with Hector, he is impatient. With Athos, he comes across as wise and concerned. Teodor's explanation of Bramimond strongly hints he was born a normal human being like others, but his dark magic skills turned him into what he is today.

(Source: Fire Emblem Wiki)