Joshua the Dog is the father of brothers Jake, Finn, and Jermaine. He and his wife, Margaret, adopted Finn as a baby. He speaks in a 1940s Mid-Atlantic accent. Joshua's personality is demonstrated as an old-fashioned manly dog who is willing to push his sons to fight, particularly when they need to.
Joshua is confirmed as deceased by Finn. He, as well as his wife Margaret have probably died prior to the events of Adventure Time. The cause of death is unknown. In "Dad's Dungeon", the hologram video shows Joshua being attacked by an Evil Monster, this may have happened while Jake was still a baby, since the last hologram shows him telling Finn he finished the dungeon. In addition, Finn and Jake did not know about the dungeon until that episode, and Finn mentions burying Joshua with Jake's help in "Billy's Bucket List", indicating that Joshua escaped the monster and died at some later date.
Furthermore, in the beginning of "Dad's Dungeon", Joshua says, "If you're hearing this prerecorded message, it means I've passed on, and my spirit sparkles guided you to its secret hiding place", which adds to the evidence that he is dead but able to send signals using his spirit.
Although Joshua did not possess stretching abilities like Jake, he was still a tough dog who created a reputation for himself in Ooo prior to his death. It can be assumed that he is a very capable warrior or extremely stealthy, as demonstrated by the fact that he was able to outsmart and break a piece of horn off Kee-Oth. Joshua was also able to capture various monsters, including the Evil Monster and put them into his dungeon.
Joshua is also proficient in other things such as knitting, which was shown in "King Worm". However, this may not be true as he was only seen doing this in a dream. Joshua knows of at least one incantation, used to slough Kee-Oth the Demon whose blood is present in the Demon Sword. In "Dad's Dungeon", he seems to create "spirit sparkles." It is unknown if this is a unique attribute or if Joshua even created them at all. He apparently knows how to make pickles.
In "Joshua and Margaret Investigations", he's shown to be quite acrobatic as he was able to perform a flip while getting to the telemarketer.
Joshua looks very similar to Jake except his fur is a darker yellow color when compared to his son's. He also wears a grey hat that resembles a fedora to hide a scar on his head that he got when he "gave birth" to Jake.
In "Joshua and Margaret Investigations", he wears a navy blue tie.