The first Ferryman is a demon called Charon. Ferrying is a lonely job, all told, particularly as most souls in modern times enter by the Gates; the lifespan of a Ferryman is thus reduced, as even demons like people to talk to.
After Charon's death, the position is filled by dm Cunard.
There are no formal qualifications for Ferryman; a demon might gravitate here if it was too weak or polite to carve a more exalted position for itself, or if it wanted to fulfil a necessary if rather ceremonial duty, or indeed preferred the solitude. No great skill (at shapeshifting, for example) is required for the job, but it helps if you can count to two.