Nereus

Nereus was the father of Amfetriti and the grandfather of Galliteya.

Biography
Nereus was spying on the Lankester. He killed a crew member, Crawford, to avoid being seen. He swam through a breach in the ship and spied on the Doctor and Callany. He brought the Doctor down into his realm and returned his TARDIS.

Nereus returned to the ship and, with his people, killed De Requin. He then collected Galliteya from the Doctor and Peri Brown. (BFA: Cryptobiosis)