Mars was always thought to be inhabited. At the turn of the century percival lowell was the biggest proponent of martian life. He built his own observatory in arizona to study mars. He believed he saw a network of 'canals' on mars, presumed to be an irrigation tool for the dry deserts of mars. He also thought changes in green markings on the planet were seasonal changes in vegetation. Other observers with larger telescopes disagreed. They said lowell's smaller telescope didn't adequately show detail on mars. Lowell's views were embraced by a public who wanted the romance of a dying culture fighting their arid planet's woes.
It later turned out that the canals were an illusion and the green markings were just surface color changes created by wind-blown dust. Lowell did make one lasting contribution though. He believed in the existence of another planet beyond neptune. Many years after his death, pluto was discovered at his lowell observatory by clyde tombaugh (who has just recently passed away in january at age 90).
Mars is an easy naked eye target. It's reddish-yellow hue is a standout. It's brightness varies more than most of the planets.
Mars is one of the more interesting planets through the telescope. At closest approach (occurring about every two years) even a small telescope will show it's polar caps. A moderately sized telescope will show a wealth of surface detail. This takes a little experience though. Sometimes a planet-wide dust storm will occur obliterating all markings