before they became the Dabu, what race were they?

It's Dabus, in singular and in plural. What do you mean before they became Dabus? They are a race themselves.

The dabus are the servants of the Lady of Pain, the enigmatic ruler of Sigil. They float above the ground and speak in rebuses, symbols strung together to spell out words. They tear down walls and construct streets under the unspoken command of the Lady. That is their purpose.

[This message has been edited by Taluntain (edited October 13, 2001).]