Franklin was Jack Harkness' father. (TW: Adam)
he lived on the boeshane peninsula with his wife, jack and gray.
he used to play what looked to be cricket (TW: Adam)
during the attack by the 'worst creatures in existence' he ordered jack to flee with gray but jack let go of grays hand and eventually he was killed by the creatures
jack returned to his home to find his mother cradling his corpse.
he later appeared to jack when jack was hunting a weevil in the sewers.
the memory changing alien, adam masquarading as one of the team made jack remember his past. franklin was included in that illusion.