BJ Penn, one of the most accomplished and beloved fighters of all time, will re-enter the Octagon at UFC Fight Night on Sunday in Phoenix.
Penn, 38, is set to end a retirement that began in mid-2014, when he announced he was walking away from the sport following an ugly defeat to Frankie Edgar. Even before Penn made it official, it was clear he had battled with the idea of retirement for several years.
His opponent, Yair Rodriguez, is in a different place in his career. Rodriguez is 24 and considered one of the most promising prospects on the UFC roster.
ESPN.com is here to tell you everything you need to know heading into Sunday.
Yair Rodriguez (9-1) vs. BJ Penn (16-10-2), featherweights
Odds as of Jan. 12: Rodriguez -470; Penn +375
"The Prodigy" returns, mostly to feed "addiction"
When Penn suffered a one-sided TKO loss to Edgar in July 2014, it was in the name of one thing: closure.
In many ways, that fight never made sense. Penn was moving down to featherweight for the first time, to face an opponent he'd already lost to twice.
If the fight did have a purpose, it was supposed to ensure Penn would never lose sleep at night, dreaming about the "what if's" of some fantasy featherweight title run. Edgar's dominance was supposed to close that rabbit hole in Penn's mind for good.
"I really needed to find out," Penn admitted that night. "If I didn't make this happen for myself I would have always wondered. I guess, I just needed closure."
That closure didn't last. Penn managed to stay away for about 18 months, before announcing he had joined Jackson-Wink MMA and was planning a comeback.
He says he avoided the gym completely during the time off, mostly because he figured once he stepped back in, a comeback would be inevitable.
"I was just hanging out at the beach, watching my kids, regular stuff," Penn said. "It's weird, I wasn't thinking about coming back. I wanted to stay out of the gym the whole time because I knew if I went to the gym, I would get good results and I'd want to fight again."
Penn, 38, was initially supposed to come back last April, but was pulled after he became the focus of a criminal investigation (no charges were made). He was then scheduled to fight in June and again in October, both of which were ultimately canceled.
So, it has been a bumpy road back to the Octagon, but Penn has seen it through. He has talked about winning an unprecedented third UFC title -- he's a former champion at lightweight and welterweight -- and says he allowed himself to return because renowned trainer Greg Jackson told him a third title was possible.
Ultimately though, it's hard to watch Penn's comeback -- this time against a 24-year-old prospect -- without feeling a sense of deja vu.
He's here because he can't not be here, still dreaming about questions he received the answers to years ago.
"I'm addicted to standing right in front of somebody and going for it," Penn said. "You can't find that anywhere else. After this is done, the only thing that will be as exciting will be replaying the memories in my head.
"I want to see the fight, how I perform and if everything I'm thinking is correct. I want to test the theories I have and of the people coaching behind me."
Key stats
Yair Rodriguez:
9-1 record in MMA career (5-0 in UFC)
Seven-fight win streak dating to Feb 2013
Two wins by knockout, two wins by submission
Performance bonuses in three of past four fights
64 percent significant strike defense, according to FightMetric
BJ Penn:
16-10-2 record in MMA career (12-9-2 in UFC)
Three-fight losing streak, 1-5-1 since 2009
Former UFC welterweight and lightweight champion (only one of three champions in multiple divisions)
Five hours, 18 minutes of UFC fight time (fifth-most all-time)
74 percent takedown defense, according to FightMetric
Breakdown
Sad career walk-offs are not uncommon in the fight game. Few athletes get to leave the cage or ring on a high note.
That said, Penn's final fight against Edgar was a disaster.
Who can forget the awkward, upright stance of that night, which robbed Penn of punching power and made him even more vulnerable to Edgar's takedowns? None of the staples of Penn's lifelong success -- his debilitating jab, guard passes, confidence -- were present in that one.
It's tempting to throw that whole performance out when handicapping this matchup. Whether you choose to do that or not, there are plenty of unknowns surrounding Penn ahead. He has been under new coaching at Jackson-Wink MMA in Albuquerque, New Mexico, but will also have longtime coach Jason Parillo in his corner.
On paper, Penn presents plenty of potential problems for Rodriguez, who is just a tad bit wild in the Octagon. His volume is off the charts and he proved capable of maintaining that volume over five rounds in his last fight against Alex Caceres.
Rodriguez hits a lot of air though, and Penn will have plenty of opportunities to counter box. It really is a classic veteran versus prospect fight. Rodriguez is going to make mistakes -- his youth and aggressive style make that inevitable -- but does Penn have enough in the tank to capitalize?
It's worth noting this is the biggest fight of Rodriguez's career, by far. He's a young kid from Mexico, climbing into the cage against an opponent he admits he once idolized. Penn has won just one fight in the past seven years, but he's still a dangerous finisher and this division certainly suits him better than welterweight did. Whether or not Penn's legacy actually gives him a mental advantage on the night of the fight will be interesting to see early.
Prediction: Rodriguez by second-round TKO.