The first example that we know of is the arc "The Invisible Empire" from Federal Men by Jerry Siegel and Joe Shuster in New Comics #8-10 (1936).
https://ultraboy8888.files.wordpress.com/2014/08/adv_9__federal_men_001.png?w=206&h=300
http://1.bp.blogspot.com/-usUIgdyXcJ8/TsNG64fTk5I/AAAAAAAAYdA/Y1mh8gmjrS0/s1600/New+Comics+010-63.jpg
http://brad-ricca.com/history-proves-again-and-again-siegel-and-shusters-atlantic-rim/https://ultraboy8888.wordpress.com/2014/08/09/new-comics-9-federal-men/http://fourcolorshadows.blogspot.com.br/2011/11/federal-men-siegel-and-shuster-1936.htmlhttp://dccomicsartists.com/superart/JOE_SHUSTER2.htmhttp://mikegrost.com/federal.htmThe brazilian comic strip Audaz, o demolidor by Aruom (scripts) and Messias de Mello (art) debuted in A Gazetinha #445 (December 17, 1938), in this issue, Superman made debut in the country. The first arc was published until 1940.
http://3.bp.blogspot.com/-4rM3AhgSRjw/URbt-R__t8I/AAAAAAAAA5k/ZDF_-ZyPb8w/s320/2396.jpg
Between 1948 and 1949, another arc by Lindbergh (script) and Messias de Mello (art) was published in the same supplement.
http://4.bp.blogspot.com/-6CmDNldlhWg/US_qBmGMrJI/AAAAAAAABQo/wfNY8DwlZBc/s1600/2860.jpg
http://artistamessiasdemello.blogspot.com.br/https://www.flickr.com/photos/messiasmello/http://www.messiasdemello.com.br/according to Overstreet's Comic Book Price Guide, Bozo the Iron Man was the first robot to appear in a comic book cover, but, however, not he, before he and the Audaz. In fact, the first robot in a magazine cover was a robot created by Hergé (creator of Tintin) in Les Aventures de Jo, Zette et Jocko, more precisely the story arc "Le 'Manitoba' ne répond plus", published in Le Petit Vingtième in 1937.
http://www.hoodedutilitarian.com/wp-content/uploads/2013/02/Bozo-the-Iron-Man.jpg
http://1.bp.blogspot.com/-IZvPuL3WmQw/U5eo6V0dTmI/AAAAAAAAAh4/lqMeaSrteIo/s1600/manitoba.jpg
http://www.toonopedia.com/bozorobo.htmJackie Law and the Boy Rangers
Clue Comics #v1#3-4 (1943)
http://2.bp.blogspot.com/_eFUN75lZPhw/SrwLCtOl-AI/AAAAAAAAAmI/CPFk2yoq5JE/s400/rangersandlocoomggiantrobotman.jpg
according to Wikipedia:
"The 1880 Jules Verne novel La Maison à vapeur (The Steam House) featured a steam-powered, piloted, mechanical elephant. One of the first appearances of such machines in modern literature was the tripods of H. G. Wells' famous The War of the Worlds (1897). The novel does not contain a fully detailed description of the tripods' (or "fighting-machine", as they are known in the novel) mode of locomotion, however it is hinted at: "Can you imagine a milking stool tilted and bowled violently along the ground? That was the impression those instant flashes gave. But instead of a milking stool imagine it a great body of machinery on a tripod stand."
Mecha were popularized by Japanese anime and manga. The first humanoid giant robot is Tetsujin 28-Go, introduced in 1956. Tetsujin was controlled externally via remote control by an operator. The first occurrence of mecha being piloted by a user from within a cockpit was introduced in the manga and anime series Mazinger Z by Go Nagai, first published in 1972"
http://en.wikipedia.org/wiki/Mechahttp://static.giantbomb.com/uploads/scale_small/6/65050/1345259-mazingerz.jpg
First japanese giant robot:
"Kagaku Senshi New York ni Shutsugen su" by Ryūichi Yokoyama
(1943)
http://i39.tinypic.com/2i260l3.jpg
source:
http://www.sf-encyclopedia.com/entry/mecha