The second issue of Secret Origins features the first appearances of Supergirl, Green Lantern and the Atom.
For many years Superman thought he was the only survivor of his native planet Krypton. Then one day that assertion is shattered when another spaceship shatters on the Earth and out pops a teenage girl wearing a similar outfit to his own! Welcome to Earth, Superman's cousin Kara, who was also sent into space before the planet Krypton exploded, but has reached the planet by a more circuitous route. Hence the reason it took the girl who will be known as Supergirl much longer to reach our world than Kal-El took. With the help of Superman, his cousin takes on the identity of orphan Linda Danvers - wearing a brown wig to disguise her blonde hair and deflect any suspicion which may accompany Linda never being around at the same time as Supergirl. Beats glasses I suppose!
Abin Sur was the Green Lantern of space sector 2814. Mortally wounded in battle, Sur's spaceship crash lands on the Earth - from where the alien sends his power ring to search for a man without fear who has the capability of taking his place. The ring finds test pilot Hal Jordan and brings him to Abin Sur who explains what has happened. Placing the ring on his finger, Jordan point its at Sur's power battery and declares his sacred oath, "In brightest day, In blackest night, no evil shall escape my sight. Let those who worship evil's might beware my power, Green Lantern's light!" Hal then realises that he can use his will power to create whatever he can think of with the power ring. Hence another crime fighter is born.
On a field trip with students, University scientist Ray Palmer finds himself cut off in a cave containing the strange "White Dwarf Star." Coming into contact with the White Dwarf Star enabled Palmer to shrink himself to a tiny 6 inches in height. The tiny Palmer used his small size to escape the cave he was trapped in and then rescue his students. Back in his laboratory, Palmer used the White Dwarf Star Material to make himself a costume, which automatically fit him as he pressed his palms and reduced his size to six inches again. Although his size was reduced, Palmer retained his full 180lb strength - thus was born the Tiny Titan who became known as ...The Atom!
Showcase #22 (Green Lantern)
Showcase #34 (The Atom)
Action Comics #252 (Supergirl)