We talk about Ash's dad but several of his companions also had missing parents

Both of Misty's parents are missing

Brock's mom was missing during the original series but eventually appeared

Both of Tracey's parents are missing

Dawn's dad is missing

Both of Iris's parents are missing

Both of Cilan's parents are missing

Serena's dad is missing

Clemont and Bonnie's mom is missing

Mallow's mom died

Lillie's dad was missing but was found eventually