Grandfather Halfling was an incarnation of the Doctor active during the Second War in Heaven.
Biography
Grandfather Halfling was present during the founding of the City of the Saved and was an old friend of its creator Compassion. Halfling was only permitted to enter the city because of his half human, half Time Lord lineage.
In the city the Grandfather founded House Halfling, which campaigned for the rights of half-humans, who were treated as an underclass. Halfling recruited his old friend Amanda Legend Lefcourt to represent the House in the Chamber of Residents while the Grandfather himself would often leave the city to participate in the War. (PROSE: The Book of the War)
It was implied that Grandfather Halfling once took Melicia Clutterbuck outside of the city to share adventures with him. (PROSE: Of the City of the Saved...)