By the end of Philosopher's Stone, Harry knows quite a few things about James that are likely to have endeared him.
Hagrid liked him (see also, why Harry hates Slytherin)
‘Sorry,’ he said. ‘But it’s that sad – knew yer mum an’ dad, an’ nicer
people yeh couldn’t find – anyway –
He left Harry a pile of money
All Harry’s – it was incredible. The Dursleys couldn’t have known
about this or they’d have had it from him faster than blinking. How
often had they complained how much Harry cost them to keep? And all
the time there had been a small fortune belonging to him, buried deep
He was an impressive Quidditch player
‘Your father would have been proud,’ she said. ‘He was an excellent
Quidditch player himself.’
He hated Snape.
‘Oh, he does,’ said Quirrell casually, ‘heavens, yes. He was at
Hogwarts with your father, didn’t you know? They loathed each other.
His father looks a lot like him
The tall, thin, black-haired man standing next to her put his arm around her. He wore glasses, and his hair was very untidy. It stuck up at the back, just like Harry’s did.
He died (bravely) defending Harry and Lily
‘How touching …’ it hissed. ‘I always value bravery … Yes, boy, your
parents were brave … I killed your father first and he put up a
courageous fight … but your mother needn’t have died … she was trying
to protect you … Now give me the Stone, unless you want her to have
died in vain.’
He was a lovable scamp
Dumbledore’s eyes twinkled. ‘Useful things … your father used it
mainly for sneaking off to the kitchens to steal food when he was
James Potter put his life on the block to save an enemy
‘Well, they did rather detest each other. Not unlike yourself and Mr Malfoy. And then, your father did something Snape could never forgive.’
‘He saved his life.’