Who is Ian Rider from Stormbreaker and what is their importance?

Ian Rider is Alex's uncle. Ian takes Alex in as an infant after the death of his brother and sister-in-law. When Ian is not traveling for work, he takes Alex on trips that include trips overseas and to do things such as rock climbing. After Ian's death, the MI6 begins watching Alex and they come to the conclusion that Ian had been preparing him for the day when Alex would become a spy himself. Clearly Ian prepared Alex well because he survives the same mission that killed Ian.