Robo has a very varied arsenal and can do backup duty as The Smart Guy when Lucca isn't around, The Big Guy when Ayla isn't, and even The Medic when Marle isn't.
The Ace / Sixth Ranger: Magus, who can use all four elements and is a fast and reasonably powerful fighter as well.
YMMV on which of the seven are the most important five. This always includes Marle, Lucca, Frog and Crono. It sometimes includes Magus (for magic users), Ayla (for strength), or Robo (for roles).
Our hero. A young boy from the village of Truce in 1000 A.D. who lives with his mother and cat. Doesn't say much, but becomes quite the hero after being sucked back in time.
The Hero Dies: In a break from RPG tradition, Crono actually dies fighting Lavos before the end of the game, and you don't even need to revive him to win.
Heroic Mime: Subverted in one of the endings, where he actually gets 2 lines.
Shock and Awe/Light 'Em Up: Crono eventually learns lightning-based magic (changed to "light"-elemental, even if the spell is still called Lightning, in the DS Updated Rerelease). It's supposed to be "Sky" or "Heaven", which is why he also gets revival magic and Luminaire, the über Holy spell. Light was likely the closest fit without actually using "Heaven".
One of Crono's friends from 1000 A.D. Lucca is very good with gadgets, a trait she inherited from her father, Taban. She discovered small pockets of distortions in time (which she dubbed "Gates") after an accident at Leene Square hurled Marle back in time to 600 A.D.
The princess of Guardia Castle in 1000 A.D., and daughter of King Guardia XXXIII. Fed up with the trappings of royal life (i.e. not being able to go anywhere without her father's approval), she runs off and bumps into Crono at the Millennial Fair. Her real name is Nadia, but she prefers to be called Marle.
She also becomes hellbent after Crono dies to bring him back, along with Lucca. When the whole world is telling her "you have to let go", she says Screw Destiny one more time.
Crash into Hello: She first bumps into Crono at the Millennial Fair, dropping her pendant.
Crutch Character: While she's the main healer for the most part, all her healing techs are single target only unless they're combined with somebody else; for this reason, she tends to get ditched as a healer (and thus just plain ditched) once Frog and/or Robo's magic stats get high enough for their wide-angle heal beams to be worthwhile.
Dub Name Change: Her real name was Marledia in the Japanese version.
Personality Powers: A notable aversion: Marle is hot-headed, impulsive, and passionate, yet her elemental focus is all ice.
Pimped Out Dress: The royal dress she wears in the past, a similar dress she flings off in the present, and a Fairytale Wedding Dress in the good ending cutscenes on re-releases of the game.
Samaritan Syndrome: She's one of the friendliest people you'll ever meet, puts on no airs whatsoever regarding her rank, and her idealism is what leads her to declare that they should Screw Destiny and change history by opposing Lavos.
Spoiled Sweet: Marle has a few aspects of this. She could hardly be called shallow, but her sheltered upbringing has left her a trifle naïve, she nurses a definite sweet tooth, and she knows how to give orders to get her own way — and, if that doesn't work, how to throw proper tantrums.
Squishy Wizard: She can't take as many punches as the others. A funny sort of subversion is that she has the highest natural magic defense of anyone in the party, which makes her one of the easiest characters to keep alive in the final battle against Lavos.
A renowned warrior of the kingdom of Guardia, hailing from 600 A.D. He was placed under a curse by Magus, and has sworn to defeat to avenge his best friend Cyrus.
Absurdly Sharp Blade: In one of the most famous examples of an exaggerated version of this trope, he slices an entire mountain in half with the Masamune. A MOUNTAIN.
Badass: And HOW! Probably the most badass out of the heroic characters, despite his unassuming form or because of said form!
Expy: His human form is Vegeta with green hair. In the good-ending cutscenes, anyway. In the ending after you kill Magus his hair is long and green.
Failure Knight: Was unable to prevent Cyrus' death at the hands of Magus. The quest chain prior to his recruitment is the party's effort to get his confidence back.
He Cleans Up Nicely: In one of the endings, Lucca sees Glenn in his human form. She then starts drooling, wondering why he never told anyone he was "such a dish."
Incredibly Lame Pun: His Slurp special allows him to, quite literally, lick his allies' wounds.
An R-Series robot from 2300 A.D. (serial number R-66Y, real designated name Prometheus) that Crono and friends find in the Proto Dome, abandoned by his creators. He joins the party after Lucca repairs him in order to help them kill Lavos.
Arm Cannon: He uses it in several techs. And in one case, "uses it" means "fires Frog out of it."
Fastball Special: He can throw Frog with the Blade Toss attack and Ayla with the Spin Kick attack. Frog can also throw him with a Bubble Hit attack, trapping Robo in a bubble, moving him over the enemy and then popping it so Robo's heavy metal body lands on the monster.
Frickin' Laser Beams: Robo's other type of attack, fired from his body. Strangely, they're shadow-elemental.
Healing Shiv: His lasers can be tuned to Shadow-element implements of destruction, or healing rays.
Laser-Guided Amnesia: No pun intended. Does not initially remember much about his setting.
Mighty Glacier: Has the highest HP of any character, yet moves quite slowly. (Although he has rollers in his feet, used in his Tackle attack.) One of the sidequests he can undertake upgrades his speed, however.
Plot-Relevant Age-Up: During the Fiona sidequest, Robo spends 100 years re-cultivating the forest. His remains are stored in a chapel built in his honor. Once Lucca powers him up, Robo reveals that he has gained a new perspective on life.
Robo Speak: His text boxes include an electronic noise to indicate this. The Japanese version also has him speak in katakana, a common way to show mechanical speech.
Rocket Punch: Robo's first special attack, and the wired variant.
Situational Sword: His ultimate weapon, the Crisis Arm, deals damage dependent on the last digit of his HP. If it is 0, it does no damage. If it is 9, it deals a lot of damage.
The Slow Path: Takes it on purpose to help Fiona grow a forest. This renders him centuries older than the other characters (assuming he wasn't already centuries old to begin with).
Ayla
A strong, burly, female tribal chief from 65,000,000 B.C. As one of the first humans, she is on-hand to discover Lavos' terrible destructive power.
All Amazons Want Hercules: Averted. Ayla's love interest is Kino, who is most certainly NOT a Hercules.
Then again, considering that official art makes her look mid-20s and him look barely teenaged, her attraction to him might suggest a different trope altogether...
On the other hand, she first shows interest in Crono because he kicks tons of Reptite ass. And by "shows interest in," we mean "pushes him against the cliff wall and starts dry-humping him." However, she later says that she prefers Kino, so...
But on the gripping hand, she does say that she became chief because she's the strongest, and if she dies then Kino will be the chief, so he may actually be the second-strongest member of the Ioka tribe.
Badass Normal: The only human character without magic.
Also the only character to not equip weapons. Her "weapons" slots are her fists, which are periodically upgraded at level milestones.
Bi the Way: Seen by some in this line: "Me like strong person. Man, woman, both like!" and her Kiss and Charm abilities work on allies and enemies (respectively) regardless of gender.
Fastball Special: She throws Crono in the Falcon Hit attack, while Robo and Crono throw her in the Spin Kick and Drill Kick attacks. Frog is a borderline example with the Bubble Hit attack, as he traps her in a bubble, directs her over the enemy, and pops it so she can land on the monster.
Lightning Bruiser: Ties for fastest player character with Magus, and has the highest strength of any character.
Ms. Fanservice: Aside from her outfit, several of her abilities openly trade on her sex appeal. An early prerelease version of the game even gave her "Kiss" ability the name "Arousal"!
Pregnant Badass: Some of her comments, and her throwing up after Nizbel is defeated, implies that she is in the very early stages of pregnancy during the game. There is a debate, however, if the throwing up was because of morning sickness or if she was just hung over from the party the previous night.
If she was pregnant, the fetus is now dead from alcohol poisoning. Yes, Fridge Horror is a dish best served cold.
Shout Out/Name's the Same: Shares her name with the protagonist of Jean Auel's Earth's Children series, who was also a prehistoric woman. She lived less than a million years ago, however (you know, because there were no humans around in 65,000,000 B.C. in the real world).
Thanks for the Mammary: Does it unabashedly to Marle during Marle's Side Quest. Ayla claims that Marle isn't "ready" to have her own kids yet (of course, Ayla was comparing Marle's chest to her own, so the bar is a little high...)
An evil wizard from 600 A.D. but actually from 12,000 B.C., worshiped by the monsters of Medina Town, and wielder of many forms of dark magic. He plans to summon Lavos, the being destined to destroy the world.
Casting a Shadow: He's the only magic-user in the game explicitly stated to be shadow-elemental. His ultimate spell, Dark Matter, is a particularly notable example of the trope and his SECOND strongest spell is a black hole.
Crutch Character: Magus joins very strong, and his stat growths are top notch (indeed, he'll max most stats before anyone else, even the non-magical ones) but he has no healing abilities or double techs, and very few and usually Awesome, but Impractical triple techs.
After Lavos dumps him back in 12,000 BC, he assumes the mantle of the "Prophet". Averted in that while he is in fact manipulating the queen, he's just doing it to kill Lavos.
Duel Boss: The second time around, if you choose to confront him with Frog in your active party.
Early Bird Boss: The first fight with him, it's an elemental magic reliant brawl, at which point few if any of your party members has their level 2 spells. Frog and Crono are forced for this fight, so Lightning and Water are covered, but you can't possibly cover all of the elements, since only Lucca can use Fire magic and only Robo can hit with Shadow element (and it's a rather weak spell against a boss to boot). Taking either could leave your healing a bit weak, and Magus can be a very hectic boss requiring constant healing, but taking Marle to better cover your healing will leave you only able to cast Lightning and Water magic. And God help you if you forgot to take Frog to meet Spekkio.
Everyone Calls Him Barkeep: In the SNES translation and Japanese version, "Magus" and "Maoh" (literally "demon king") are his names, respectively. Averted in the DS translation: "Magus" is a name he gave himself, while his title is "Fiendlord."
Fire, Ice, Lightning: He uses these as his barriers, along with a shadow one he very rarely uses and you probably won't be able to damage. When he joins you, his three starting techs are the level 2 spells of these elements.
Right from the beginning, Magus' name keeps being dropped.
When he kills Cyrus and turns Glenn into Frog during Frog's flashback, the theme of Zeal Palace plays for the first time in the game. Later it's revealed that Magus actually lived in Zeal Palace, as the child prince of Zeal.
Four is Death: Guess how many bosses you fight in his castle. Come on, guess. Four.
He Who Fights Monsters: As a child, he blocked out his magical power because he hated what it was doing to his mother and sister. After he was sent to 600 A.D., he embraced that same power in order to destroy Lavos, becoming much like his mother in the process.
Heel Face Turn: You get to choose whether or not to let him join your party after Crono's death.
Hidden Villain: Doesn't rear his head until roughly halfway into the story, and then only in flashback.
Jerkass: It's a matter of much debate whether he's truly one or simply adopting a Jerkass Façade.
On the one hand, he was just a little kid when his mother went insane and caused him to be sucked into a time gate, which does not seem necessarily like jerkass-spawning experiences. On the other, he was raised by fiends since then, and they might have had some negative effect on him.
Master of None: In terms of his non-Shadow magic anyway. He starts with the level 2 versions of lightning, fire and ice magic, making him very versatile for some of the endgame bosses. However, Crono, Frog and Lucca will eventually learn stronger spells of their own elements. He's still party's the master of Shadow magic, mind you.
Pet The Cat: After he joins your party, Alfador recognizes him, indicating that he hasn't changed so much that he'd seem like a different person to his cat.
Prophetic Name: "Janus" is named for the two-faced Roman god, implying dual identities.
Redemption Demotion: Magus is still very powerful all around, especially compared to Lucca and Marle, your other two dedicated mages, but he's weaker when compared to his boss fight.
Justified in that Lavos drains his power when he tries fighting it at the Ocean Palace.
Retroactive Precognition: Magus is able to disguise himself as a great prophet after some accidental time travel knocks him over twelve thousand years into the past. It also helps that he landed in his home time period.
Woobie, Destroyer of Worlds: Even though Janus was kind of a Royal Brat, it's hard not to feel sorry for a child thrown tens of thousands of years into the future and adopted by literal monsters.
The Worf Effect: Gets rather thoroughly defeated when he takes on Lavos solo.
This happens every time: implied in the original timeline in the middle ages, on-screen in the Ocean Palace, and on-screen in the DS version's bonus ending against the "Dream Devourer."
Lavos
An Eldritch Abomination that has destroyed the world several times over. It was first spotted (and named) in 65,000,000 B.C.
Bigger Bad: Doesn't have any spoken lines or interactions, and doesn't really advance the plot, with other antagonists like Magus and Queen Zeal doing that.
Bishonen Line: If by "bishonen" you mean faceless alien pod-thing.
Colony Drop: The X factor which wipes out the Reptites, ushering in an ice age. Thus the reign of man begins. It's like a cooler version of the asteroid that killed the dinosaurs in Real Life.
The Corruption: Lavos doesn't interact with individuals or take any notice of them, it just makes its power available to be drawn upon, and its power warps those who use it (both humans and entire civilizations) into wickedness (and in one case, physically as well as mentally).
Humanoid Abomination: Its final form appears to be a humanoid Ancient Astronaut capable of warping time and space. Actually, the core seems to be one of the two Lavos Pods, so... averted?
Final Boss Preview: Getting pummeled by Lavos in the Ocean Palace. In the first playthrough, you will likely have no chance to attack before he kills you instantly. Or, alternatively, skipping ahead to the Day of Lavos.
Somewhat Zig-zagged in that Lavos' shell is not, in fact, the True Final Boss. Additionally, Lavos is beatable the first time, during a New Game Plus.
Flat Character: There really isn't much to it. Kinda like how there's not much to a slug, only slugs probably have a fear response.
Hero Killer: It kills Crono at the Ocean Palace. Actually, it kills your whole party, and then kills Crono For Real.
Monster Is a Mommy: The party encounters several "Lavos Spawn" on Death Mountain. The characters don't talk about it (except Belthasar in his sparkly-light-diary-thingy but it is definitely played more for horror than for sympathy: Lavos is planning to hurl its children into space so they can destroy more worlds.
Leader of the Reptites of 65,000,000 B.C., a race of lizard creatures that consider themselves the natural enemies of the earliest humans.
Ambiguous Gender: In the original SNES version, Azala's gender is never brought up (mostly since all Reptites look the same). Nizbel II identifies Azala as female in the DS remake.
Save the Villain: Attempted by Ayla. As Lavos falls from the sky, Ayla tells Azala to come with them to safety by flying away on Dactyls, but Azala is resigned to her fate and refuses.
The Social Darwinist: She ultimately decides that if Reptites are doomed to die, so be it.
Her asking Ayla to "take care of this world" may indicate that the Reptites opposed humans because they thought that the humans' primitive mannerisms made them unsuitable as the dominant species. Ironically, Lavos, the most primitive-minded character of all, compensates for this by placing humanity on the evolutionary fast-track.
Queen Zeal
Leader of the magical civilization that thrived (and was eventually destroyed) in 12,000 B.C. She used the Mammon Machine to draw upon Lavos' power to keep the floating city alive. Has two children, Janus and Schala.
Abusive Parent: Extremely abusive and neglectful to Janus and Schala. Thanks entirely to Lavos' influence. As Janus says, "She's not our mother," indicating that she may have been less of a bitch before.
The Dragon: After the defeat and possible Heel Face Turn of Magus, she becomes the primary human enemy and Lavos' main servant. Interestingly, Lavos does not seem to even acknowledge her because Lavos is a force of nature, not a human enemy.
HP To One: Queen Zeal is fond of casting her Halation spell on your party, which makes this happen to everyone. Less commonly used when she transforms.
Immortality Immorality: She manages to achieve her desire for eternal life, at the cost of her sanity... and the lives of her children and most of her subjects... and the magic powers of the ones who survived... basically, everything but her body and her powers.
Sequential Boss: Your first fight with her is inside the Black Omen. Then she goes One-Winged Angel, and you teleport up to the roof for the final confrontation.
Bad Boss: After his defeat, two of his soldiers can be found along with the survivors and when talked to they will mention that Dalton was a "terrible master" and "stingy with the coin too."
Dragon Their Feet: Abandons the Ocean Palace and Zeal itself aboard the Blackbird when the power of Lavos proves more than he expected. Turns out doing this was a very good call on his part.
The Starscream: When the Queen is believed to be dead after the Floating Continent crashes and floods the world, Dalton quickly establishes himself as "King Dalton". It doesn't last very long.
Yakra
One of a long line of monsters that has opposed the Guardia royal family since 600 A.D.
Dragon Ascendant: After defeating Magus, Ozzie becomes the new leader of the fiends. He sets up his own fortress similar to Magus's, and if you travel to Medina village in 1000 A.D. and you'll find them warshipping his statue instead of Magus's.
Hypercompetent Sidekick: Ozzie's always a joke, but Slash and Flea are respectable enemies when you first meet them in Magus' Castle. It doesn't last, however.
It's implied that the female form we see is just an illusion as well.
Flea: Man or woman, it's all the same. Power is beauty, and I'm deliciously strong!
Mother Brain
Mother Brain was the central computer that linked the domes and factories together. After the planet is ruined by Lavos, Mother Brain becomes responsible for the uprising of robots over humans.
What Happened to the Mouse?: It's never really explained what happened to her in this game. This very trope is the reason why Radical Dreamers, and later Chrono Cross, (because Kato wasn't satisfied with the former) were created.
The master of war. He gives Crono, Lucca, Marle and Frog their magic abilities.
Bonus Boss: His last form (a pink Nu) can only be fought if at least one member of the party is level 99, and is the hardest enemy in the game(at least in the SNES version).
The Guru of Life (Melchior, The Guru of Time (Gaspar) and the Guru of Reason (Belthasar) who originally lived in 12000 BC. They try to stop Queen Zeal harnessing the energy of Lavos. When Lavos is summoned it sends the three of them along with Janus to different periods in time.
Badass Grandpa: Melchior in particular, since when you meet him at his home in 1000AD, it's sandwiched between a town full of hostile monsters, and a cave full of hostile monsters. And this guy makes frequent trips to the mainland.
Chokhov's Gunmen: All three of them, if you traversed the Abandoned Sewers and entered Keeper Dome before you needed to. Twice for Melchior, though the second time it's already become clear that he's not ordinary.
All-Powerful Bystander: In Chrono Cross, thanks to Clarke's Third Law. He can summon up holograms, breeze in and out of the Arcadia Dragoon's HQ, and even appear at whim.
Big Good: Ultimately, his overall goal is good, and managed to keep the peace in El Nido and save time itself.
