9. The Collector
Assuming that Ultron has his eyes on one of or some of the Infinity Stones (which he could well have, given that his artificial intelligence should give him access to databases such as those of S.H.I.E.L.D which house data about them), the Collector - who will be an established Marvel Cinematic Universe character by that time - could take an interest in him. Ultron has come to the attention of the Collector in the comic books, so it wouldn't be the first time that the two had come in to contact - Ultron's creation Jocasta was taken as a trophy by the intergalactic being. We don't really know what the Collector is going to bring to the table in the MCU, so it's hard to say how he could fit in to Ultron's plans - but it's for that reason that we can't rule him out of a team-up with the robot. In the comic books, he's an incredibly powerful being - one of the Elders of the Universe - but that hasn't been shown yet in the MCU. However, if he is of that level of power, he could be a big help to Ultron.