Leonard 'Len' Reynolds arrived in Emmerdale in 2001, to visit his only son Sean following the death of his wife and Sean's mother, Eileen. Len's presence was a great comfort to his son and his family. Sean and his wife Angie were going through difficulties in their marriage and having Len as a mediator was helpful. However, the marriage was destroyed when it was revealed that Angie was having an affair with Cain Dingle and Sean left to start a new life with his girlfriend, Lady Tara Oakwell. Len stayed behind to help Angie rebuild her life, at the request of his granddaughter Ollie. Len kept a close watch on his grandchildren - not knowing that soon he would be required to take on a more pivotal role in their lives.
In November 2002, Angie was killed in a car crash whilst attempting to set Cain up in order to get him out of her life, leaving Len to look after Marc and Ollie. Marc went to live with his father but Ollie chose to stay with Len and her boyfriend Danny Daggert moved in with them. Len enjoyed living with them and was sad when Ollie moved away to go to university. At the same time, Len developed feelings for local pensioner Edna Birch but she did not reciprocate. However, he found love again with flamboyant newcomer Pearl Ladderbanks. Enchanted by Pearl's sunny personality, Len moved in with her. Pearl, however, was hiding a secret. Her son, Frank Bernard Hartbourne, whom she had said was a financial advisor, was released from prison - after serving a sentence for rape. When Len found out the truth, he was horrified and it looked like their relationship was over but he realised what Pearl had been through and he agreed to stand by her. Having nowhere else to go, Frank joined Pearl in Emmerdale but when his arrival was announced in the local paper, the villagers were outraged and turned against Pearl and Len. Only vicar Ashley Thomas and Edna stood by them. Devastated at being treated so cruelly by their neighbours, the couple decided to leave Emmerdale but Frank refused to ruin his mother's life any further and moved to a bail hostel in Leeds, after he was viciously assaulted by Scott Windsor and Syd Woolfe. Len and Pearl decided to stay and try and rebuild bridges with their neighbours.
Len was delighted for Pearl when her grandson Owen Hartbourne visited from Hong Kong and even agreed to start saving to visit him there but Pearl's saving got out of hand. She started investing in an internet scheme that was revealed as a scam and lost her money, not to mention the money her friends had also invested. Feeling responsible, Pearl paid her friends the expected dividends regardless but this got her into serious debt as she had borrowed a large sum from her boss, Eric Pollard. Pearl repaid the loan but Eric insisted on charging her for repaying it early and started blackmailing her so she was doing additional work from home to pay him back. However, when Len found out about this, he punched him and thought that the matter was resolved. But although Eric still charged Pearl the early settlement fee that he said must be paid or he would report Len for assault. Pearl decided to keep this from him and Len had no idea that her debts had spiralled even further. Their relationship ended when Len found out about Pearl's lies and she left the village in disgrace. Two months later, she returned with the intention of winning her respect back and reuniting with Len but Len finally admitted to Pearl that he was in love with Edna, despite the fact that she wasn't interested. She vowed to stand by him regardless and Len proposed. Pearl accepted and the couple began planning their wedding.
During this time, Len was aware that Edna had somehow discovered a forged structural report within the Kings River Explosion that incriminates the family's role behind the incident; he persuades her to go through with reporting the evidence to the HSE, but the results were insufficient due to the family's resourcefulness as instigated by Edna's boss Tom King. A few days later, Len finds out that Edna has become a recluse ever since her report against the Kings were unsuccessful and later discovers that Tom had recently blackmailed her with the knowledge that her son had belonged to her sister whom Edna had refused to give back; this revelation prompted Edna to throw Len out of her home when she insisted on being alone. Enraged, Len punches Tom before being punched back and a confrontation breaks out between them until Tom's youngest son Carl arrives to break up the fight; with Len promising Tom that he will get his comeuppance for both Edna's isolation and his role in the Show House Explosion. Len continued to clash with Tom up towards Christmas Day 2006 and was even more frustrated to discover that Edna received an invitation to Tom's upcoming Christmas wedding with Rosemary; this motive drove Len into coming over to his wedding day that ended in a tragedy when Tom fell off his bedroom window to his death.
On 17 May 2007, Len, with the other villagers, attended a village pageant to celebrate Emmerdale's 500th birthday. Pearl was supervising activities, had failed to include Edna. Len was disappointed with Pearl and went to check Edna was alright and he comforted her. Len then returned to the church hall with his friend, Sandy Thomas. Whilst the celebrations were occurring outside, Len died in his chair of a heart attack, aged 70. He was found by Sandy, who had been bringing Len a drink. Sandy thought Len was asleep and tried to wake him until he checked Len's pulse and realized he had died. Sandy, knowing it was too late, told a shocked Pearl, who was devastated. Jo Stiles, who had become a close friend of Len's through Danny, begged Donna Windsor-Dingle to keep on trying to resuscitate him, but to no avail. An ambulance arrived to take Len's body away while Pearl tried to contemplate her loss in private and Sandy comforted Betty and Edna. As news of Len's death spread around the village, Len's body was driven away in an ambulance whilst Katherine Jenkins sang him out, although as she was closing the pageant, unaware of the death that had occurred in the village.