Nós não sabemos

Nenhuma fonte oficial falou sobre isso, e com um filme tão antigo, eu duvido que eles irão. Existem várias teorias na web.

A partir de O jogador:

This would be because Finger was voiced by none other than Vin Diesel.

Diesel went uncredited for this small role. Though Besson has stated that he does not want to make a sequel, I would be very much in favour of Finger being introduced so we can have Riddick and Korben Dallas kicking butts together on screen.

O IMDB Trivia afirma:

Who plays the voices of Finger, Korben's mother, and Mr. Shadow? No one was credited for these roles, and there's no clear evidence as to who was used. However, some have speculated that it was Jill Mullan, who is credited under Other Crew for "special thanks". Others have suggested that Finger sounds like Bill Nunn or Vin Diesel but neither of these have been confirmed.

In respostas,

Sounds a lot like Nick Chinlund, who also starred with Bruce Willis in Tears of the Sun.

E esse aleatório Imgur link afirma que era Glenn Fleshler:

It's rumored on the 'net that it's Vin Diesel. Not that Vin wouldn't have nailed it, but it's not him. It's this man: Glenn Fleshler.

Receio que não haja uma resposta conclusiva.