Who was Skyresh Bologolam ? What was galbet's role in the story ?

Skyresh Bologlam was the high-admiral.

I swore and subscribed to these articles with great cheerfulness and content, although some of them were not so honourable as I could have wished; which proceeded wholly from the malice of Skyresh Bolgolam, the high-admiral: whereupon my chains were immediately unlocked, and I was at full liberty.

"Galbet" translates to high-admiral. This is not a separate character, but rather Bologlam's title.

That minister was galbet, or admiral of the realm, very much in his master’s confidence, and a person well versed in affairs, but of a morose and sour complexion.