It's about time I introduce Clarke, while it may seem he's introduced at random, he's actually been in the works since the series' beginning.

Simply put Clarke and Claire were two very closely aged siblings, Clarke being only a a year and 8 months older, and as a result they gained very close bond through the chaotic childhood they had together.

Their father Lewis Zera was a researcher constantly traveling in search of the legendary Mew pokemon. Eventually it lead them to Kanto, where the siblings stayed with Professor Oak a friend and colleague of their father. Shortly after Lewis went off on an expedition to South America to see if he could have any success finding mew there.

Being separated from their father, devastated the two and became increasingly isolated since they had never learned how to make friends, due to their constant traveling. While Oak was kind, they were barely more than strangers.

Eventually Clarke being the more adventurous of the two managed to get an interest in pokemon training, and using rumors of a Kanto Mew sighting set off to capture it, not for fame, but to bring dad back. He never returned, and despite an exhaustive search and multiple failures to contact Lewis, Claire was now alone.