Do I believe intelligent life exists on other planets? Absolutely. The odds of us being the only (or even the first) intelligent species to evolve in the universe are so ridiculously small as to essentially be zero. Do I believe that extraterrestrials have visited Earth in the past? Maybe. It’s entirely possible that they have. I haven’t seen any rock-solid evidence of it myself yet, though, so I’ll reserve judgement until I do see some rock-solid evidence.