Mateo moved to Pine Valley from Texas with his parents and younger sisters in 1995. He got a job at the Valley Inn as a waiter where he met and fell in love with Hayley Vaughan who was engaged to Alec McIntyre. One night while partying on the beach with a bunch of his co-workers, he stumbled upon a very distraught, wedding gowned, Hayley Vaughan. Hayley had run away from her own wedding to Alec. Matt consoled Hayley who soon realized that she was really in love with Mateo. Matt had a brief "romance" with Taylor Cannon in order to pump information from her regarding her nefarious plans for Noah and Julia. Once Noah and Julia's innocence were proven, Mateo proposed to Hayley and they moved in together. Mateo has quit his job at the Valley Inn and he and Hayley have bought Hal's Bar and turned it into "their baby", Holidays. Hayley has told Mateo that she is quitting Enchantment to become his full time partner at Holidays
Matt has always been the very conservative, morally upright young man that the Santos family and Hayley depend on. Mateo was the golden boy until his wife Raquel and their son Mateo Jr. (Max) appear out of nowhere. Mateo was unaware that he had a son and believed his marriage to Raquel had been annulled. Now a bigamist, this negated his marriage to Hayley and stopped all discussions of them having a child of their own. After a long time struggle with Raquel attempting to regain Mateo's heart, she finally gave up and returned with Max to Texas. But before she left she told Hayley that she had slept with Mateo since reappearing in his life in Pine Valley. This information along with Mateo's jealous rage for Ryan Lavery and his attempt to get Hayley to drink a shot of vodka (she's an alcoholic) drove Hayley away from Mateo and straight into the arms of Ryan Lavery.
Hayley and Ryan's relationship never went beyond a kiss --- although it came pretty close. Ryan knew in the back of his mind that Hayley and Mateo would get back together. Mateo and Hayley's relationship took another turn when Hayley refused to tell Mateo that she and Ryan didn't sleep together. She allowed him to believe that they had. Mateo also misled Hayley by not letting her know that he'd been the one who'd plucked Ryan out of a car after he'd had an accident. Hayley knew that Mateo hated Ryan and assumed that Mateo had walked away and let Ryan in the car to die.
Hayley found herself in great peril --- unconscious and trapped in a burning warehouse. Mateo sensed that something was wrong and followed a tip that Hayley was inside the building. He arrived just in the nick of time and freed her before any serious harm was done. This rescue brought the two back together. Mateo and Hayley resumed their courtship, even as the spirits of their rocky past surfaced. In January 2000, Mateo proposed to Hayley. Arlene, Hayley's mother, showed up in March and Mateo and Hayley both feared that she'd keep them from happiness. Arlene did manage to cause them some headaches, but in June 2000, Mateo and Hayley were finally wed --- for real.
In the months ensuing, Mateo took on a part-time gig as producer for Hayley's style show, "Wave." When Arlene revealed that she had gotten pregnant, Mateo suggested that he and Hayley adopt Arlene's child. Arlene turned them down and later miscarried the baby, further dashing Mateo and Hayley's hopes of starting a family.
Hayley and Arlene's volatile relationship exploded in the fall of 2000 when, after a boatload of people were drugged with the libido enhancing drug Libidozone, Hayley "killed" her mother. Hayley caught Arlene in bed with a drugged Mateo and strangled her. When her body disappeared from the deck - Adam had stumbled across the body and tossed it overboard - Hayley believed that Arlene was dead. Racked with guilt, Hayley developed an alternate personality, that one her mother. She paraded around town as her mother - complete with wig and tacky clothing. The Chandler clan was haunted by Arlene's presence until Mateo figured out that Hayley had "become" her mother. Later, however, Mateo also learned that Arlene wasn't really dead after all. A newspaper article that showed a picture of one-of-a-kind necklace that Arlene had stolen from Vanessa Cortlandt the night of the yacht party told him that Arlene had survived her watery grave, made it to land and pawned the necklace for some fast cash. He tracked her down to an exotic island in the Caribbean and hauled her back to Pine Valley just in time to prevent Hayley from confessing in court that she had killed Arlene. Arlene was ordered by Adam to sign off on their marriage and leave town - never to return again.
On February 21, 2001, Hayley learned from a psychic visiting Wave that she was pregnant. On August 29, 2001, Hayley delivered a healthy baby boy after some brief complications.
Mateo's life became complicated when Proteus, a mysterious drug lord, demanded that he use SOS as a venue for drug selling. Mateo refused, but Proteus threatened Mateo's family and Mateo was forced into agreeing. However, Mateo decided to play double agent and while working for Proteus also try to smoke him out and turn him into the police. Simone Torres played the part of Mateo's mistress in order to throw Proteus off of what was really going on -- Mateo was trying to crack the drug lord's inner-ring of advisors in order to take him down. Simone, however, developed real feelings for Mateo and at one point planted a legitimate kiss on her partner. Simone felt badly and apologized profusely to both Mateo and Hayley. Hayley was able to forgive Simone's transgression, saying that she understood that Mateo was quite handsome. Mateo was jailed for a short time because federal agent Chris Stamp thought it was the only way to keep Mateo safe from Proteus. Simone leaked details of the Proteus investigation to what she believed was a publisher. As it turned out, the "publisher" was really someone working for Proteus - whose identity was revealed as Vanessa Cortlandt. Simone's leak resulted in a sniper gunning down Chris Stamp. Mateo was furious with Simone and ordered her to stay clear of him and his family. Vanessa suffered a nervous breakdown of sorts and was kept under guard at the hospital. Now free from the drug trafficking, Mateo and Hayley were able to return to the more important things in life - like raising their son.
Life took an unexpected turn in late 2002 when Hayley was told that there was an interest in syndicating her Wave talk show. Hayley didn't want to take the job offer because it would mean relocating to California. She and Mateo bickered back and forth for a bit before eventually agreeing to leave Pine Valley.
Hayley and Mateo returned to Pine Valley in January 2010 to film a documentary about the small town, which had just been named "The Best Town In America" by the Atlantic Press. Hayley revealed that her children were growing up fast. Enzo was a teenager and Max had been sent to a boarding school in Utah because he'd started hanging out with the wrong crowd and butting heads with Mateo.